JP2002167240A - Method of washing crystallized glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of washing a crystallized glass substrate removing remained abrasive particles effectively without generating tiny depressions on the surface of the substrate. SOLUTION: This method of washing to remove abrasive particles from a crystallized glass substrate having abrasive particles remained on the surface comprises dipping the crystallized glass substrate 14 into a washing liquid 12 in a washing tank 10 and washing with ultrasonic wave having frequency of 600 kHz or higher emitted from an ultrasonic wave generator 11 equipped at the bottom of the washing tank 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a crystallized glass substrate, and more particularly to a method for cleaning a crystallized glass substrate for a magnetic disk used for a hard disk or the like.

[0002]

2. Description of the Related Art Aluminum alloy substrates have been widely used as magnetic disk substrates used for hard disks of computers. In recent years, with the demand for higher storage capacity, glass substrates with less deformation and excellent surface smoothness have been put to practical use. As a glass substrate for a magnetic disk, an amorphous (amorphous) glass substrate such as soda lime glass and aluminosilicate glass and a crystallized glass substrate are known.

An amorphous glass substrate has excellent surface smoothness, but it has been pointed out that alkali metal ions contained therein are easily eluted and may corrode a magnetic film. On the other hand, in the crystallized glass substrate, most of the alkali metal ions are taken into the crystal phase, the alkali metal ions do not elute, and the magnetic film does not corrode. For this reason, a crystallized glass substrate is particularly promising as a substrate for a magnetic disk, which is increasingly required to have a smaller size and a higher storage capacity. In the production of this type of glass substrate, generally, after polishing the surface of the substrate, which has been disc-processed to a predetermined size, with abrasive grains, cleaning is performed to remove polishing particles remaining on the glass surface. The cleaning method is performed by pre-cleaning the polished glass substrate, and then performing ultrasonic cleaning while immersing the glass substrate in a cleaning solution such as an ammonium fluoride solution.

[0004]

However, according to the cleaning experiment conducted by the present inventor, it is possible to remove the adhered particles while maintaining the flatness in the amorphous glass substrate, but it is possible to remove the adhered particles in the crystallized glass substrate. It turned out that many fine dents are generated on the substrate surface later. The reason for this is
In a crystallized glass substrate, a crystal phase and an amorphous phase are mixed, and fine crystals fall off from the substrate surface during the cleaning process. Such minute depressions on the substrate surface hinder the function as a magnetic disk.

[0005] The present invention has been made in view of such circumstances, and it is possible to effectively remove abrasive particles remaining and attached without generating minute depressions on the surface of a crystallized glass substrate. It is an object to provide a cleaning method.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for cleaning a crystallized glass substrate, wherein the polishing particles are removed from the crystallized glass substrate having abrasive particles adhered to the surface thereof. It is characterized by performing ultrasonic cleaning at a frequency of 600 kHz or more while immersing.

As the cleaning solution, an ammonium fluoride aqueous solution having a concentration of ammonium fluoride of 0.5 to 1.0% is preferably used.

[0008]

According to the present invention, while the crystallized glass substrate is immersed in the cleaning liquid and ultrasonically cleaned at a frequency of 600 kHz or more, the etching action by the cleaning liquid and the micro-vibration action of the cleaning liquid by the ultrasonic cleaning are synergistic. In addition, it is possible to effectively remove the polishing particles remaining and attached without generating minute depressions on the surface of the crystallized glass substrate. In particular, when the frequency of the ultrasonic waves is set to 600 kHz or more, cavitation that occurs when low-frequency ultrasonic waves are used can be prevented. For this reason, even if a cleaning liquid having an etching action is used, local etching can be prevented,
Fine crystals do not fall off the substrate surface during the cleaning process.

As described above, an aqueous solution of ammonium fluoride having a concentration of ammonium fluoride of 0.5 to 1.0% is preferably used as described above. When the concentration of the cleaning liquid is lower than the above value, the cleaning effect is reduced because the etching action is weak. When the concentration is higher than the above value,
Since the etching action is too strong, uneven cleaning is likely to occur on the substrate surface, and the tendency of crystals to fall off the substrate surface is increased.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram showing an example of a device configuration for implementing the present invention. A cleaning solution 12 having a predetermined concentration is applied to the cleaning tank 10, and a crystallized glass substrate 14, which is an object to be processed, is immersed in the cleaning solution 12 by a substrate transfer device 16. An ultrasonic generator 11 for irradiating ultrasonic waves having a frequency of 600 kHz or more toward the cleaning liquid 12 in the tank is attached to the bottom of the cleaning tank 10.

A gutter 18 for overflowing the cleaning liquid 12 is provided at an upper portion of the cleaning tank 10. The cleaning liquid 12 discharged from the gutter 18 is sent from a pipe 20 to an adjustment tank 22. A chemical solution tank 24 for replenishing the chemical solution is connected to the adjustment tank 22 via a pipe 28 having a control valve 26. In addition, in order to maintain the liquid level of the adjustment tank 22 constant,
A conduit 30 for supplying pure water is connected.

A pipe 32 is connected to the bottom of the adjusting tank 22.
The cleaning liquid 12 in the adjustment tank 22 is circulated to the cleaning tank 10 by a circulation pump 34 provided in a pipe 32. In addition, a filter 38 and a concentration meter 40 for detecting the concentration of the chemical solution are provided in the pipeline 36 on the discharge side of the circulation pump 34. The detected value of the concentration meter 40 is sent to the controller 42, and the controller 42
The opening of the control valve 26 is controlled so that the detected value becomes a predetermined value. In addition, a conduit 44 for discharging the cleaning liquid out of the apparatus is branched from the conduit 36, and the cleaning liquid can be renewed by intermittently or continuously discharging the cleaning liquid from the conduit 44. .

In the above configuration, the crystallized glass substrate 14 to which the abrasive particles have adhered is mounted on the substrate carrier 16 and immersed in the cleaning liquid 12 in the cleaning tank 10 for about 3 minutes. The crystallized glass substrate 14 is subjected to an etching action by the cleaning liquid 12 whose concentration is adjusted within an appropriate range and a micro-vibration action of the cleaning liquid by ultrasonic cleaning at a frequency of 600 kHz or more, so that a slight depression is formed on the surface of the crystallized glass substrate 14. The polishing particles remaining and adhered are effectively removed without generation of the particles.

When an aqueous solution of ammonium fluoride having a concentration of 0.5 to 1.0% of ammonium fluoride is used as the cleaning solution, the so-called soft etching proceeds to the so-called substrate because the concentration of the chemical solution is low. . Further, since the pH of the cleaning solution in this concentration range is 6 to 7, the zeta potential of the glass surface and the zeta potential of the abrasive particles are both negatively charged and repel each other. For this reason, even when the crystallized glass substrate 14 after the cleaning is pulled up from the cleaning liquid 12, it is possible to suppress the abrasive particles that have been peeled off from re-adhering to the substrate surface.

[0015]

Experimental Example 1 Using a crystallized glass substrate for a 2.5-inch magnetic disk, the frequency in ultrasonic cleaning was changed, and the effect of the frequency on the surface roughness of the substrate was examined. The crystallized glass substrate as a test material has a sufficiently flat surface secured by a predetermined polishing, and has an arithmetic average roughness Ra of 0.1.
The thing of 22 nm was used. The experimental conditions were as follows: an aqueous solution having a concentration of ammonium fluoride of 0.5% was used as a washing solution;
The crystallized glass substrate was immersed in a cleaning liquid at a liquid temperature of 23 ° C., and irradiated with ultrasonic waves of various frequencies for 3 minutes. The intensity of the ultrasonic wave at this time was about 0.5 W / cm ² in each experiment.

The surface roughness of each test material after washing was measured with an atomic force microscope, and the arithmetic average roughness Ra was determined. The result is shown in FIG. As is clear from FIG. 2, even when the same cleaning liquid is used, the arithmetic average roughness Ra of the substrate after the cleaning changes depending on the frequency of the ultrasonic wave. At 100 kHz or less, the arithmetic average roughness Ra is 1 compared with that before the cleaning. It is more than .5 times, and it can be seen that unevenness of etching is caused by ultrasonic cleaning. On the other hand, at 600 kHz or more, the arithmetic average roughness Ra is 1.1 times or less as compared with that before cleaning, and the etching unevenness can be minimized. In addition, in the observation result by an image with an atomic force microscope, at 100 kHz or less, minute dents (dents having a depth of about 5 nm) were observed at 10 to 30 / μm ² at the surface of the substrate, but at 600 kHz or more, The number of minute depressions was 10 / μm ² or less.

[0017]

EXPERIMENTAL EXAMPLE 2 A 2.5-inch crystallized glass substrate for a magnetic disk was polished with a polishing solution, and the surface to which abrasive particles were attached was used as a test material. The polishing conditions at this time were such that cerium oxide having a particle size of 0.4 to 0.8 μm was used as a polishing material, and cerium oxide suspended in pure water at 10% by weight was used as a polishing liquid. Polishing pressure 50kgf / c by polishing machine
Polishing was performed for 20 minutes under the conditions of m ² and a table rotation speed of 40 rpm. The effect of ultrasonic frequency on particle removal when the polished test material was subjected to ultrasonic cleaning in the order of pure water and a cleaning solution was examined. As a result, the frequency of the ultrasonic wave is changed from 45 kHz to 1.0.
Even when the frequency was changed in the range of 00 kHz, the number of particles of 0.1 μm or more remaining on the substrate was not much different, and it was found that the higher the frequency, the better the particle removal performance.

[0018]

EXPERIMENTAL EXAMPLE 3 The same test material used in EXPERIMENTAL EXAMPLE 2 was immersed in pure water and subjected to ultrasonic cleaning (frequency 750 kHz, cleaning time 3 minutes), and then a primary cleaning solution having a hydrofluoric acid concentration of 50 mg / L. And subjected to ultrasonic cleaning (frequency 750 kHz, cleaning time 3 minutes) as a test sample. This test sample was subjected to ultrasonic cleaning with a secondary cleaning solution. An aqueous solution of ammonium fluoride was used as the secondary cleaning solution, and the concentration of each solution was changed to examine the effect of the concentration of the secondary cleaning solution on the cleaning. Other cleaning conditions were unified for each test, and the frequency of the irradiated ultrasonic wave was 750 kHz.
z, the washing time was 3 minutes.

Each test sample after washing was measured with an atomic force microscope, and the arithmetic average roughness Ra was determined. In addition, 0. 0 remaining on the surface of each test sample after washing.
The number N of particles having a size of 1 μm or more was visually counted. Table 1 shows the experimental results.

[0020]

[Table 1]

As is clear from Table 1, the preferred concentration of the secondary cleaning solution having a small arithmetic average roughness Ra after cleaning and a small number N of residual particles is such that the concentration of ammonium fluoride is 0.1%.
It is in the range of 5 to 1.0%. In the other concentration ranges, one of the arithmetic average roughness Ra after washing and the number N of remaining particles is deteriorated. In addition, the test No. with a large arithmetic average roughness Ra. In No. 4, a large number of minute dents (dents having a depth of about 5 nm) were observed on the surface of the substrate also in the observation result by the image with the atomic force microscope.

[0022]

According to the cleaning method of the present invention, fine dents do not occur on the surface of the crystallized glass substrate.
The remaining abrasive particles can be effectively removed.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of a device configuration for implementing the present invention.

FIG. 2 is a graph showing experimental results of Experimental Example 1.

[Explanation of symbols]

 10 cleaning tank 11 ultrasonic generator 12 cleaning liquid 14 crystallized glass substrate

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 5/84 G11B 5/84 Z F-term (Reference) 2H088 FA21 HA01 MA18 MA20 3B201 AA02 AB01 BB04 BB05 BB85 BB92 BB93 CB01 CC21 4G059 AA08 AC03 BB04 BB16 4H003 BA12 DA05 DA15 DC04 EA05 FA15 FA21 5D112 GA08 GA14 GA27

Claims (2)

[Claims] 1. A method for cleaning a crystallized glass substrate, comprising removing the abrasive particles from a crystallized glass substrate having abrasive particles adhered to a surface thereof, wherein the crystallized glass substrate is immersed in a cleaning solution while a frequency of 600 kHz or more is applied. A method for cleaning a crystallized glass substrate, comprising: performing ultrasonic cleaning on the substrate. 2. The method for cleaning a crystallized glass substrate according to claim 1, wherein said cleaning solution is an aqueous solution of ammonium fluoride having a concentration of ammonium fluoride of 0.5 to 1.0%.