JP2006351081A - Grinding method of magnetic disk substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grinding-processing method in which quality of products is improved by preventing dirt of a grinding pad and clogging caused by grinding and preventing variation of quality of coarseness of a ground surface. <P>SOLUTION: The grinding method of a glass substrate for a magnetic disk includes at least a process in which the glass substrate for the magnetic disk is ground and a process in which the glass substrate is rinsed after grinding. The grinding process includes a finish-grinding-processing-process using colloidal silica as a main component of grinding grains. The method is characterized in that the rinse process is performed while rinse liquid is applied without stopping a surface plate directly after this grinding, the rinse liquid used in this rinse process is pure water including surfactant, further, pH is adjusted to 8-12 by adding alkali. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for polishing a glass substrate for an information recording medium for use in a magnetic disk that is a magnetic recording medium for a hard disk device.

  Hard disks are becoming smaller and larger in capacity year after year. For this reason, the density of magnetic recording media (hereinafter also referred to as magnetic disks) is increasing, and the flying height of the magnetic head is also becoming smaller. Under such circumstances, improvement of the surface accuracy of the magnetic disk substrate is required. In order to improve the surface accuracy of the magnetic disk substrate, it is required to reduce the substrate surface roughness, reduce the slight waviness of the substrate, and reduce defects on the substrate surface such as micro scratches in the polishing process of the magnetic disk substrate. Further, a substrate having no residue of abrasive grains or polishing residue is required.

  In order to improve the surface accuracy of the magnetic disk substrate, a polishing cloth (pad) having a smaller hole diameter has been used. Hard polishing pads have been used. Under such circumstances, the abrasive particles and debris are likely to stay and / or adhere to the pores of the polishing pad, and continuous polishing causes the pad to become dirty and clogged. Since this causes variations in the quality of the roughness of the processed surface, it is necessary to periodically perform pad dressing.

  However, it is difficult to completely remove the abrasive particles and debris adhering to the pad by the pad dressing, and the abrasive particles and debris accumulate on the pad surface with the number of times of polishing. During polishing, these rub against the substrate surface, which causes the quality of the substrate surface to become unstable.

  For example, a polishing process of a Ni—P plated aluminum alloy substrate is performed in two stages, and alumina is used as the polishing agent in the first stage and colloidal silica is used in the finishing process in the second stage. Here, a rinsing method and a rinsing liquid have been studied so as not to bring the first-stage alumina and grains into the second-stage processing step. Patent Documents 1, 2 and 3 are examples thereof, and even recently, a more excellent rinse agent has been demanded, and development is in progress.

  Further, for example, there is Patent Document 4 regarding finish polishing of a glass substrate. In this document, a glass substrate is rinsed with pure water after polishing, and then the substrate is washed with an alkaline aqueous solution having a pH of 12 or less in order to remove colloidal silica on the surface of the glass substrate. Addition of a neutral or nonionic surfactant is disclosed.

  Further, Patent Document 5 discloses a semiconductor wafer cleaning method and a cleaning apparatus that can be used in a semiconductor wafer cleaning process. In particular, this document discloses a method and an apparatus that can remove particles firmly attached on a semiconductor wafer and can easily perform self-cleaning after cleaning. Further, although this document discloses the use of a surfactant as a cleaning liquid, the cleaning process of this document relates to a cleaning process after a rinsing process after polishing or a scrub cleaning process by brush cleaning.

JP 2000-144193 A JP-A-10-152675 JP 2004-182800 A JP 2004-63062 A JP-A-8-71511

  As described above, various studies have been made on the cleaning after polishing. In the rinsing process immediately after the final polishing of the glass substrate, in order to prevent destabilization of the quality of the glass substrate surface due to pad contamination. The rinsing method has not yet been fully examined.

  In the rinsing process, the present invention prevents contamination of the polishing pad and clogging caused by polishing, thereby preventing variations in roughness quality of the polished substrate surface due to the occurrence of such contamination and clogging. And it aims at providing the grinding | polishing processing method which can improve the quality of a product.

  The present invention relates to a method for polishing a glass substrate for a magnetic disk. This method includes at least a step of polishing a glass substrate for magnetic disk and a step of rinsing the glass substrate after polishing, and the polishing step includes a finish polishing step using colloidal silica as a main component of abrasive grains. The rinsing step is performed immediately after this polishing while flowing the rinsing liquid without stopping the surface plate. The rinsing liquid used in this rinsing step is pure water containing a surfactant, and further added with alkali. The pH is adjusted to 8-12.

  In the polishing method of the present invention, after the rinsing step, additional rinsing can be performed with a second rinsing liquid adjusted to pH 8 to 12 by adding alkali to pure water.

  By using the polishing method of the present invention, it is possible to obtain a substrate having a stable surface roughness (Ra) and to reduce the frequency of pad replacement.

The present invention is described in detail below.
The glass substrate that can be used in the present invention is used, for example, as a substrate for a magnetic information recording medium such as a magnetic disk having a disk shape with a circular hole in the center. The material for the magnetic recording medium glass substrate is not particularly limited, and examples thereof include soda lime glass, aluminosilicate glass, borosilicate glass, and crystallized glass. These glass substrates can be manufactured by a conventional procedure such as a float method, a downdraw method, a redraw method, or a press method.

  As described above, high-density recording is achieved by reducing the distance between the surface of the magnetic recording medium and the head for reading and writing information on the magnetic recording medium. When the distance between the surface of the magnetic recording medium and the head is narrowed, if irregularities exist on the surface of the glass substrate for magnetic recording medium, the irregularities are also formed on the magnetic recording portion formed of the magnetic film formed on the substrate. The head may come in contact with or interfere with this unevenness to read data, and the recorded information may not be read accurately, the head may be damaged, or the magnetic recording section may be damaged, causing problems. There is. In order to prevent such problems, attempts have been made to suppress the occurrence of unevenness by polishing the glass substrate for magnetic recording media with a highly accurate polishing process. However, there is a demand for a polishing method that can maintain the quality stability.

  The present inventors have examined the cause of the formation of such irregularities, and one of the causes for the formation of irregularities on the surface of the glass substrate is that the abrasive grains used in the polishing step in the rinsing step are those of the polishing pad. It has been found that such a contaminated or clogged polishing pad damages the glass substrate due to contamination or clogging, and continuous polishing. It is difficult to remove contamination from such a contaminated or clogged polishing pad or to completely remove clogged abrasive grains. In addition, replacing a contaminated or clogged polishing pad with a new one every time it is contaminated or clogged leads to an increase in cost.

  The inventors of the present invention have found a polishing method that prevents such inconvenience, thereby preventing variations in the quality of the polished surface roughness due to the occurrence of contamination and clogging and improving the quality of the product. In the polishing method of the present invention, the polishing process on the surface of the glass substrate includes a finish polishing process using colloidal silica as a main component of the abrasive grains, and the rinsing process immediately after the polishing process is performed without rinsing the surface plate. The rinsing solution is pure water containing a surfactant, and the pH is adjusted to 8 to 12 by adding an alkali.

  By including such a step, the method of the present invention can remove the abrasive grains (colloidal silica) used in the finish polishing step from the glass substrate surface and at the same time prevent the abrasive grains from being deposited on the polishing pad. As a result, contamination or clogging of the polishing pad can be prevented even when finish polishing is performed continuously for a long time, and variations in the quality of the glass substrate surface due to contamination or clogging of the polishing pad can be prevented. It becomes possible.

  The polishing method of the present invention includes at least a final polishing step and a rinsing step immediately after this. In the present invention, prior to the finish polishing step, the glass substrate is subjected to conventional processing such as cutting out the glass substrate and rough polishing processing of the cut out substrate.

  In the polishing method of the present invention, first, a disk-shaped glass substrate is cut out from a sheet-like glass plate, and the outer diameter dimension and inner diameter dimension thereof are set to predetermined lengths, and then the following polishing treatment is performed on the surface of the glass substrate. The polishing treatment may be performed by either a single wafer method in which glass substrates are polished one by one or a batch method in which a plurality of glass substrates are polished at one time. The method is used.

  In the polishing process, first, lapping is performed on the surface of the glass substrate. This lapping is performed to set the thickness, flatness, and parallelism of the glass substrate to predetermined values, and to remove large defects such as large waviness, chipping (chipping), and cracking (crack).

  After lapping, generally, a two-step rough polishing process is performed on the surface of the glass substrate. This rough polishing process is performed in order to remove lap marks (microcracks) and improve the surface condition, and conventional conditions and methods can be applied. For example, a hard polisher (for example, a hardness (type A) defined in JIS K6253-1997 is 75 to 95) or the like is used for the first step for rough polishing the surface of the glass substrate. A soft polisher (for example, hardness 60-75) is used for the process of this.

  As the abrasive for rough polishing, for example, the first stage has an average particle size of about 1.2 μm, and the second stage has an abrasive having a particle size of several hundred nm or less dispersed in water as a solvent to form a slurry. Is used. Examples of the abrasive include alumina abrasive grains, rare earth oxides such as cerium oxide and lanthanum oxide, zirconium oxide, manganese dioxide, aluminum oxide, and colloidal silica. Of these, rare earth oxides are preferred because of their excellent polishing efficiency, and cerium oxide is more preferred among the rare earth oxides.

  In this rough polishing, the glass substrate has a surface roughness (Ra) of less than 0.5 nm, preferably Ra of less than 0.3 nm.

  In the present invention, for example, the rough polishing step is performed by rotating the glass substrate held on the surface plate while rubbing the slurry containing the above-mentioned abrasive grains, and abutting the polishing pad and rubbing the surface of the substrate. it can.

  Next, finish polishing is performed on the surface of the glass substrate. This finish polishing is performed in order to make the surface state smooth and high quality.

  In this final polishing step, a polishing pad such as foamed urethane or nonwoven fabric can be used to polish the surface of the glass substrate.

As the polishing agent in the final polishing step, a suspension obtained by dispersing particles having silicon dioxide (SiO ₂ ) as a main component and having an average particle diameter of 150 nm or less, preferably colloidal silica, in a solvent is used. The The concentration of particles in the abrasive is preferably 3 to 40% by mass.

  In the present invention, for example, while flowing a slurry containing colloidal silica in pure water, a glass substrate (roughly polished) held on a surface plate is rotated, and a polishing pad is contacted to rub on the substrate surface. Thus, the finish polishing step can be performed.

Conventional conditions can be applied to various conditions such as polishing rate, polishing time, processing pressure, surface plate rotation speed, and slurry supply amount in the final polishing process. For example, a Speed FAM 9B double-side polishing machine (5-carrier type) In the case, it is preferably in the following range.
Polishing rate: 10 to 100 nm / min
Polishing time: 1 to 20 minutes Processing pressure: 40 to 120 g / cm ²
Surface plate rotation speed: Upper 6-15 rpm, Lower 20-40 rpm
Slurry supply amount: 50-250cc / min

  Next, a rinse process is performed immediately after the finish polishing process. This rinsing step is performed in order to wash away the abrasive remaining from the surface of the glass substrate and the polishing pad, and to prevent accumulation of abrasive and polishing debris on the surface of the polishing pad.

  The rinsing liquid for rinsing the glass substrate includes an alkali and a surfactant. In particular, in the present invention, water is used as a solvent, and a rinse solution prepared in the range of pH 8 to 12 with an alkali is used.

  The surfactant is at least one selected from the group consisting of an anionic surfactant and a nonionic surfactant. The anionic surfactant is preferably at least one selected from the group consisting of a low molecular weight compound such as a carboxylate, a sulfonate, a sulfate ester salt, and a phosphate ester salt, and a polymer compound. The nonionic surfactant is preferably selected from the group consisting of polyhydric alcohols, polyoxyethylene alkyl ethers, fatty acid ethylene oxides, polypropylene glycol ethylene oxides, aliphatic amines and ethylene oxide compounds of aliphatic amides, and polyoxyethylene fatty acid esters. At least one selected.

The alkali is preferably at least one selected from the group consisting of NaOH, KOH, Na ₂ CO ₃ , Na ₂ SO ₄ , K ₂ CO ₃ , K ₂ SO ₄ , and an organic alkali salt. The pH of the rinse solution of the present invention is adjusted by this alkali.

  The content of the surfactant in the rinsing liquid varies depending on the type of the surfactant, but it is 0.05 to 3% by weight in the case of Toho Chemical manufactured by Toho Chemical Industry or Kao Clean Through. The alkali is added in an amount that provides the desired pH.

The rinsing step of the present invention is performed immediately after the finish polishing step by rubbing the surface with a polishing pad while supplying the rinsing liquid of the present invention instead of the abrasive. In the present invention, it is preferable to perform the rinsing step while rubbing the glass surface with a polishing pad without stopping the surface plate while flowing the rinsing liquid. Various conditions such as the rinsing time, processing pressure, surface plate rotation speed, and slurry supply amount are not particularly limited as long as the object of the present invention is achieved. The following ranges are preferred.
Rinse time: 0.5 to 5 minutes Processing pressure: 10 to 50 g / cm ²
Surface plate rotation speed: Upper 3-15 rpm, lower 10-40 rpm
Rinse solution supply amount: 0.5 to 2 L / min

  In the rinsing step of the present invention, the polishing pad is preferably dressed with a brush carrier or the like after a predetermined number of finish polishing and rinsing.

In this invention, it is preferable to perform a post-rinsing process following said rinse process. This is a polishing pad in which the surfactant remains after rinsing, and when the next polishing is performed, the original polishing characteristics of the slurry cannot be obtained, and adverse effects such as a decrease in rate and micro waviness of the polishing surface may appear. Because there is. In order to prevent such a decrease, in the present invention, it is preferable to perform post-rinsing with an alkaline aqueous solution immediately after rinsing with a surfactant. This alkaline aqueous solution contains at least one selected from the group consisting of NaOH, KOH, Na ₂ CO ₃ , Na ₂ SO ₄ , K ₂ CO ₃ , K ₂ SO ₄ , and an organic alkali salt in pure water, and has a pH It has a value of 8-12. The post rinse can be performed in the same procedure as the above rinse step.

  After the rinsing step, the substrate can be subjected to ordinary procedures such as scrub cleaning using an alkaline detergent, rinsing with ultrasonic waves (for example, 1000 kHz) in pure water, and centrifugal drying as necessary.

  As described above, the polishing method of the present invention includes 1) polishing start / substrate setting, 2) polishing (for example, rough polishing + finish polishing), 3) rinsing with a surfactant-containing alkaline rinse solution, 4) polishing end / It includes at least a series of steps indicated by removing the substrate. Further, the present invention may further include 3 ') rinsing with an aqueous alkaline solution after the rinsing of 3).

  The glass substrate for magnetic disks obtained by the method of the present invention can have a surface roughness (Ra) = 0.08 to 0.25 nm.

  Examples of the present invention will be described below. In addition, the following Examples are illustrations and this invention is not limited to these Examples.

Example 1
The glass substrate was finish-polished under the polishing conditions shown in Table 1 using a slurry containing about 10% by weight of colloidal silica having an average particle size of 0.1 μm and having a pH adjusted to 9.5. Here, the substrate before the finish polishing is about Ra = 0.25 nm due to the rough polishing step in the previous step.

  At the same time as the finish polishing was completed, the supply of the abrasive (slurry) was stopped and switched to the rinse liquid, and the rinse was performed under the conditions shown in Table 2. The rinsing liquid is prepared by adding a glass substrate cleaning agent containing about 1% by weight of a phosphoric acid type surfactant (cleaning agent manufactured by Kao Corporation) to pure water at a rate of 2% by weight, and further using NaOH to adjust the pH to 10. Adjusted to 5. Every time polishing was performed four times in succession, pad dressing was performed with a nylon brush carrier.

  The substrate after polishing was scrubbed using an alkaline detergent, rinsed with ultrasonic (1000 kHz) pure water, and then subjected to centrifugal drying.

(Comparative example)
Instead of the rinsing liquid of the example, an aqueous solution in which NaOH was added to pure water to make the pH 10.5 was used. The polishing conditions and cleaning conditions were the same as in Example 1.

(Comparative evaluation of examples and comparative examples)
FIG. 1 shows the result of evaluation of the surface of the substrate polished and cleaned in Examples and Comparative Examples by AFM. AFM measurement conditions are shown below.
Measurement area: 10μm × 10μm
Resolution: 512 × 512
Scanning speed: 1Hz
Evaluation item: Surface average roughness (Ra)

  As shown in FIG. 1, the comparative example shows an increasing trend of Ra from 30 polishing batches. It is clear from the microscope and SEM observation of the pad surface that the surface roughness is increased due to the abrasive and polishing debris deposited on the surface of the pad.

  In the embodiment of the present invention, in the rinsing step, the polishing agent and polishing debris on the substrate surface are removed, and at the same time, by using a rinsing liquid having a predetermined pH and containing a surfactant, Accumulation of abrasive and polishing debris can be prevented. For this reason, it turns out that the grinding | polishing process of the board | substrate with stable quality (Ra) can be performed for up to 40 polishing batches.

(Rinse solution liquidity (pH))
The relationship between the pH of the rinse solution and the polishing / rinsing ability was investigated. The results are shown in Table 3. The rinsing liquid to which the surfactant is added provides a larger pad cleaning effect than the liquid to which the surfactant is not added. In addition, when the liquidity is pH 8 or less, the cleanliness of the pad cannot be maintained, and the residue tends to remain on the substrate itself. If the pH exceeds 12, the dispersion state of the colloidal silica becomes unstable, so that the roughness of the polished surface cannot be controlled and the variation in the surface roughness tends to increase.

  As described above, the surface roughness variation on the substrate is controlled only by adding a surfactant to the rinse liquid used in the rinse process or by making the pH of the rinse liquid predetermined alkaline. I can't. Therefore, as the rinsing liquid after polishing, a liquid in which a surfactant is added and the liquid property is controlled to pH 8 to 12 is suitable. Moreover, the rinse liquid of the present invention exhibits a particularly significant effect when colloidal silica is used in the final polishing process.

(Additional rinse)
In the polishing step of the present invention, the surfactant remains on the polishing pad after the rinsing step. However, when the next polishing is carried out with such a pad, the original polishing characteristics of the slurry cannot be obtained, and the rate is lowered or the polishing surface is reduced. Adverse effects such as small swells may appear. As a countermeasure, by rinsing with an alkaline aqueous solution immediately after rinsing with a surfactant, the remaining surfactant concentration of the pad can be reduced and the polishing characteristics can be maintained stably.

It is a figure which shows the result of having evaluated the surface after washing | cleaning of the board | substrate which grind-processed in the Example and the comparative example by AFM.

Claims (2)

  A method of polishing a glass substrate for magnetic disk comprising at least a step of polishing a glass substrate for magnetic disk and a step of rinsing the glass substrate after polishing, wherein the polishing step comprises colloidal silica as a main component of abrasive grains. Including a final polishing process to be used, and the rinsing process is performed immediately after this polishing while flowing the rinsing liquid without stopping the surface plate, and the rinsing liquid used in this rinsing process is pure water containing a surfactant. Further, a polishing method wherein the pH is adjusted to 8 to 12 by further adding an alkali. 2. The polishing method according to claim 1, wherein after the rinsing step, additional rinsing is performed with a second rinsing liquid adjusted to pH 8 to 12 by adding alkali to pure water.

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