JP2001331933A - Method for producing magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the peeling of a film in a magnetic disk device using a glass substrate. SOLUTION: A glass substrate is irradiated with plasma in an electron beam excitation type plasma device and contaminants on the glass substrate are removed using a gaseous argon-oxygen mixture under 0.4-2.7 Pa pressure of gas in plasma discharge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium used in a magnetic disk device used as an external storage device of a workstation or personal computer,
In particular, the present invention relates to a manufacturing method for reducing a defect caused by a substrate in a thin-film magnetic disk using a glass substrate.

[0002] More generally, the present invention relates to a method for cleaning the surface of a glass substrate for a laminated thin film.

[0003]

2. Description of the Related Art At present, a thin-film magnetic recording medium, that is, a magnetic disk using a laminated magnetic thin film (hereinafter referred to as "disk") is widely used as a recording medium of a magnetic disk device. The general structure of the disc is a laminated magnetic thin film on a non-magnetic substrate, such as a pre-coated film,
An underlayer film, a magnetic film, and a protective film are provided, and a lubricating film is adhered thereon.

In order to improve the performance of a magnetic disk drive,
In order to more stably store a larger amount of information, higher recording density and higher reliability have become important issues. In order to achieve a high recording density, a disk having a high coercive force and a low-noise magnetic film is used, and the recording characteristics of a magnetic head (hereinafter, referred to as a “head”) that can cope with this are improved. Further, a method of reducing the space between the disk and the head has been adopted.

[0005] By reducing the space between the disk and the head, the possibility that the disk and the head come into contact increases. Therefore, if there is contamination such as particulate foreign matter or organic thin film on the substrate, the adhesion between the pre-coat film and the substrate laminated on it decreases due to the contamination, and the contact between the head and the disk surface causes the pre-coat film and the substrate to contact. The likelihood of exfoliation at the interface increases.

Therefore, it is important to improve the adhesion between the precoat film and the substrate in order to ensure the high reliability of the disk together with the increase in the recording density. It is necessary to remove such obstructive factors from the substrate.

[0007] At present, the mainstream material of the substrate is nickel-phosphorus plated with aluminum, but the number of disks using a glass substrate whose surface is reinforced for high recording density is also increasing.

FIG. 2 shows a general sectional view of a disk manufactured using a glass substrate subjected to a surface strengthening treatment. usually,
The disc has a laminated film disposed around the glass substrate 1, but only one side is shown in this figure.

The manufacturing process of this disk is as follows. First, a cobalt-chromium alloy pre-coat film 2, a chromium alloy base film 3, a magnetic film 4, and a protective film 5 are formed on a cleaned glass substrate 1 by a sputtering method, and a lubricant is applied to form a lubricating film 6. I do.

After the disk has been manufactured in this way,
A disk that has passed the inspection of the head flying height and the number of errors of the disk (hereinafter, referred to as “final inspection in process”) is incorporated into a magnetic disk device.

A random seek test is one of the magnetic disk device inspections performed after the disk is assembled. In this test, a random seek of the head is performed for a long time in a state in which the disk is rotated and the head floats to check whether or not a read / write error has occurred. If this inspection is performed for about 100 hours, there may occur a defect that an error portion that cannot be detected by the final inspection in the process of the disk is detected.

Observation of the error portion of the disk in which such a defect has occurred indicates that the laminated magnetic thin film is entirely missing and the substrate is exposed, or that all the layers remain, but the film is swollen as a whole. Was confirmed. When the swollen portion is rubbed with a needle tip, the glass substrate is exposed. From this, it was confirmed that the film peeling occurred at the interface between the glass substrate and the precoat film.

This film peeling has a diameter of φ5 to 50.
μm, and there is a trace of the head sliding at the film peeling portion. Also, the frequency of occurrence is about one place on the disk surface, and does not reach the entire disk surface. Therefore, this film peeling is not caused by poor adhesion on the entire surface, but is caused by a local poor adhesion portion (hereinafter, referred to as “late film peeling portion”), and the head is slid on that portion. It is to do.

The results of observation and analysis of such a subsequently peeled portion are described below. In this case, the film before sliding is an example in which all the laminated magnetic thin films remain. The substrate used was a soda lime glass substrate (Model H1) manufactured by Nippon Sheet Glass G.D. Co., Ltd. The film configuration and thickness were 22 nm for a pre-coat film (CoCrZr alloy), 25 nm for a base film (CrTi alloy) from the glass substrate side, and magnetic properties. The film (CoCrPt alloy) is laminated in the order of 19 nm and the carbon protective film in the order of 12 nm.

In the evaluation of the subsequently peeled portion, a portion where the film was swollen without peeling was dry-etched with argon (Ar), and a sample in which the precoated film was slightly left but remained was used as a sample. The analysis was performed by Auger spectroscopy (hereinafter, referred to as “Auger”). Since this sample had completely remained from the precoat film to the carbon protective film, there was no contamination from the head etc. to the peeled interface, and an Auger capable of analyzing trace elements on the very surface layer with a depth of about several nm. By using
Analyze the causative substances.

FIG. 3 shows a measurement result by Auger. Auger device is DKI-6 manufactured by ULVAC-PHI
70 was used. F (fluorine) and C (carbon) were found more in the portion where the film was peeled off than in the portion where the film was not peeled off, and it was found that a fluorine-based organic substance was present.

From this observation and analysis, the mechanism of occurrence of such later film peeling is presumed as follows. A very small amount of a fluorine-based organic substance adheres to the glass substrate, a precoat film is formed thereon, and a poor adhesion portion is formed.
The thickness of the organic substance at that time was estimated to be 15 nm or less because the thickness could not be detected by the final inspection in the process of the disk. Thereafter, the head is slid for a long time on the poor adhesion portion in the magnetic disk device, so that the subsequent film peels.

Since the later film peeling occurred at the interface between the precoat film and the glass substrate, it can be concluded that the cause of occurrence was in the manufacturing process up to the film formation. FIG. 4 shows an example of a method for manufacturing a disk. After cleaning and drying, the glass substrate enters a vacuum exhaust chamber (hereinafter referred to as “load chamber”),
After vacuum evacuation, a precoat film, a base film, a magnetic film, and a protective film are successively formed on a glass substrate in this order, and then enter an open-to-air chamber (hereinafter referred to as an “unload chamber”). It is transported to the process.

The load chamber is repeatedly opened to the atmosphere and evacuated repeatedly to continue production. At the time of opening to the atmosphere, nitrogen gas from which fine particles have been removed is introduced. When the load chamber was examined, the fluorine-based oil turned into oil mist together with the nitrogen gas, flew near the load chamber and the conveyor conveyed to the load chamber, and the oil mist adhered to the glass substrate (hereinafter referred to as “surface organic Pollution "). This fluorine-based oil is indispensable as a lubricant for the operating section of the film forming apparatus.

In general, when a film is formed by a sputtering method, a method is known in which a substrate is heated in a vacuum immediately before the formation of a precoat film to remove organic contamination on the surface and to prevent a reduction in adhesion between the substrate and the precoat film. Has been taken. However, when the material of the substrate is glass, when the substrate is heated, the alkali metal of the glass component moves to the surface and the surface concentration of the alkali metal increases, so that the adhesion between the precoat film and the substrate is reduced. J. Vac. Sci. Technol. A,
Vol. 4, No. 3, pp. 532-535 (May / June,
(May / June 1986). For this reason, it has been difficult to remove organic contamination on the surface of the glass substrate by heating in a vacuum apparatus.

As a method for efficiently removing such surface organic contamination in a vacuum immediately before film formation by sputtering, there is a dry etching technique. As a dry etching technique,
It is common to generate plasma by DC discharge, RF discharge, ECR discharge, electron beam, etc., extract ions from this plasma by the action of an electric field, irradiate the sample with the ions, and remove surface organic contamination on the sample surface. Is known to. As a control method for irradiating the sample with the ions, a method of applying a bias to the sample is generally used.

However, since glass is non-conductive, it has been difficult to control the amount of ion irradiation with a bias. Also,
In the RF discharge, the controllability of the plasma density was poor. As a method capable of controlling the ion irradiation amount even in such non-conductive glass, for example, an electron beam excitation type plasma apparatus (hereinafter, referred to as "Japanese Patent Application Laid-Open Nos. 61-290629 and 63-190229"). EBEP ”) has been proposed.

According to this method, the potential difference between the plasma and the ion sheath formed at the boundary between the sample and the sample is controlled, and therefore, the amount of ion irradiation can be controlled even in the non-conductive glass. One of the features of the EBEP plasma introduced in the above-mentioned Japanese Patent Application Laid-Open No. 61-290629 is that the plasma is formed in a cylindrical shape, so that the plasma density becomes higher toward the center and has a density distribution in the radial direction. This has a problem in controlling the dry etching.

As a method for solving this problem, for example,
Vacuum, Vol. 36, No. 3, pp. 62-64 (published in 1993) has proposed a method of enlarging the area of an electrode porous portion and a method of using a magnetic shutter described in JP-A-6-28991. .

However, if the area of the porous portion of the electrode is increased, the device becomes large and it becomes difficult to mount it on a mass production device. Also, if a magnetic shutter is used, contamination such as sputtering from the portion is expected. There was a problem.

The production of a disk in a film forming apparatus is performed in a cycle of 10 seconds or less, including transfer between chambers, in order to ensure productivity, and it is desired to further reduce this time. Of this time, the time actually usable for the process is 5 seconds or less. Within this time, pressure fluctuations of about 1 Pa to about 10 ^-4 Pa are repeated by the intake and exhaust of the gas used for the process. In order to remove organic contamination on the surface of the disk substrate, there is also a problem that the treatment must be performed in a short time in such a large pressure change.

EBEP indicates that at oxygen and argon pressures of 0.026 to 1.33 Pa, the plasma density monotonically increases with increasing pressure, but decreases at higher gas pressures. No. 62-64 (1
993). Generally, there is a correlation between the plasma density and the etching rate, and the above report suggests that the etching rate using this plasma also changes with the change in the gas pressure.

However, in order to secure and improve the quality of a disk produced in a vacuum apparatus that repeatedly uses suction and exhaust instantaneously, such as in the case of disk production, fluctuations in the etching rate due to dry etching do not occur even if the gas pressure fluctuates. Establishing fewer processes has become an important issue.

[0029]

SUMMARY OF THE INVENTION The present invention relates to a method for manufacturing a thin-film magnetic disk using a glass substrate, which removes organic contaminants on the glass substrate by installing a magnetic shutter in a film forming apparatus or by using a porous electrode. It is an object of the present invention to provide a disk manufacturing method for efficiently removing a disk in a short cycle without introducing measures including an incidental problem such as an increase in the area of a portion.

[0030]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention investigates the cause of surface organic contaminants generated in a film forming apparatus in disk production, and based on the result,
A method has been found that can effectively remove the contaminants under a clean atmosphere.

That is, EBEP is used as a removing means by dry etching, and even if the gas pressure fluctuates, the mixed gas material and its composition that provide a constant effect on the etching rate for organic contaminants, and the gas pressure conditions, etc. Clarified and applied.

The etching rate was stabilized by using an argon-oxygen mixed gas as the etching gas in EBEP and setting the gas pressure in a range of 0.4 to 2.7 Pa. Further, by controlling the oxygen concentration of the argon oxygen mixed gas to 10 to 70 volume percentage,
It has been found that the removal can be performed stably in a short time, and a special effect can be obtained.

[0033]

<Embodiment 1> The processing amount and in-plane distribution of dry etching by EBEP were evaluated. EBE
As P, manufactured by Nichimen Electronics Co., Ltd. (Model: EBE
P Type II) was used. FIG. 5 schematically shows the EBEP and the vacuum apparatus. A vacuum device manufactured by Shin-Meiwa Co., Ltd. (model: VVC130S, hereinafter referred to as "prototype vacuum device") was used. As a sample for evaluating the processing amount of dry etching, in order to surely confirm the removal of organic substances,
A carbon protective film on the disk was used. Configuration is 65mm
A soda lime glass substrate (Model H1) manufactured by Nippon Sheet Glass G.D. Co., Ltd. was used as the substrate, and the film configuration and film thickness were from the glass substrate side to a pre-coated film (CoCrZr alloy).
After laminating 22 nm, a base film (CrTi alloy) 25 nm, and a magnetic film (CoCrPt alloy) 19 nm, a carbon protective film 26 nm for evaluating a processing amount is laminated as an uppermost layer (hereinafter, this sample is referred to as an “etching sample”). )
did.

The processing amount of the carbon protective film was evaluated using an ellipsometer manufactured by Photo Device Co. (model: MARY102). The measurement point was located at a radius of 21 mm.
The voltage of the acceleration power supply 17 is 50 V, and the current of the cathode power supply is 5
A.

One of the factors affecting the etching amount is the evacuation characteristics of the vacuum device. In order to examine this effect, the opening degree of the conductance adjusting gate 18 was changed while the gas flow rate was constant to adjust the pressure of the process chamber 12, and then the carbon protective film was etched by discharge, and the opening degree of the conductance adjusting gate 18 was determined. After the pressure of the process chamber 12 was adjusted by changing the gas amount while keeping the pressure constant, an investigation was performed on the case where the carbon protective film was etched by discharge.

FIG. 1 shows a constant gas flow rate (15 cm ³ (Nor
4 shows the relationship between the pressure in the chamber and the etching rate of the carbon protective film when the opening degree of the conductance adjusting gate 18 is changed under (mal) / min). A mixed gas of oxygen and argon (Ar) was used as a process gas. The volume fraction of oxygen in the gas is from 0 to 70 volume percent.

In this case, at an oxygen concentration of 10 to 70% by volume, the etching rate of the carbon protective film monotonically increases until the pressure becomes 0.4 Pa, and becomes 0.4 to 2.7 Pa.
Is almost constant irrespective of the pressure, and decreases at higher pressures.

In FIG. 6, the opening degree of the conductance adjusting gate 18 is fixed, and the gas flow rate (0 to 100 cm ³ (Norm)
4 shows the relationship between the pressure in the chamber and the etching rate of the carbon protective film when (al) / min) was changed. A mixed gas of oxygen and argon (Ar) was used as a process gas. The volume fraction of oxygen in the gas is from 0 to 70 volume percent.

Also in this case, at an oxygen concentration of 10 to 70% by volume, the etching rate of the carbon protective film monotonically increases until the pressure becomes 0.4 Pa, as in the result of FIG.
From 2.7 Pa to 2.7 Pa is almost constant and does not depend on pressure.
It decreases at higher pressures.

The results in FIGS. 1 and 6 show that when the pressure is in the range of 0.4 to 2.7 Pa, there is almost no effect of the exhaust conductance, and the etching rate of the carbon protective film is almost constant.

Next, the pressure within this range (1.0 P
a) The etching rate distribution of the carbon protective film was measured at a lower pressure (0.1 Pa) and a higher pressure (4.0 Pa). The measurement range was measured from a radius of 15 to 30 mm at a pitch of 3 mm. This was repeated every 90 °. The oxygen concentration was 70% by volume, the current value of the cathode power supply 16 was 5 A, and the voltage value of the acceleration power supply 17 was 50 V.

FIG. 7 shows 0.1 Pa, 1.0 Pa, 4.0 P
FIG. 8 shows the comparison of the etching rate at each pressure of a, and FIG. 8 shows the result of comparing the relative values when the etching rate at an angular position of 0 ° and a radial position of 21 mm is 1.

At 0.1 Pa, the etching rate is 1.
About 5 nm / sec, at 1.0 Pa about 7.5 nm / sec,
At 4.0 Pa, it was about 3.0 nm / sec.

The in-plane distribution of the etching rate is 0.1 P
In the case of a, the angle position is 0 ° and the radius is 21 mm.
An etching rate distribution of about 5% to + 30% occurs, but at 1.0 Pa, about −2 to + 2%, and 4.0P.
In a, the distribution was about -6 to + 3%.

These results indicate that the mixed gas pressure was 1.0 Pa
Indicates that the etching rate is large and the in-plane distribution is stable.

<Embodiment 2> In order to examine whether the stability of the etching rate distribution obtained in Embodiment 1 can be reproduced even when the scale of the vacuum sputtering apparatus is increased, etching is performed in a vacuum sputtering apparatus used for mass production of disks. The rate distribution was evaluated.

As a plasma device, EBEP Type
II was used. Inevac as vacuum sputtering equipment
(Model: 250B or less, “mass production machine vacuum device”) was used. Process conditions: 1.0 Pa vacuum during discharge
(Oxygen concentration 70 volume percent ratio, argon concentration 30 volume percentage ratio), vacuum of about 10 ^-4 P during transport (transport time 2.2 seconds)
a, a discharge time of 2 seconds, a voltage of the cathode power supply 16 of 50 V,
The voltage of the acceleration power supply 17 was 5 A. The process is performed repeatedly on a 9.0 second cycle.

FIG. 9 shows a schematic diagram of a mass production vacuum apparatus. The EBEP was mounted on the first station 20 of the twelve stations, and the other stations did not perform film formation by sputtering. An etching sample was put therein, and the distribution of the etching rate was evaluated.

FIG. 10 shows relative values when the etching rate is 1 and the etching rate at an angular position of 0 ° and a radial position of 21 mm is 1 as shown in FIG. These results show that even when EBEP is installed in a vacuum equipment for mass production,
This shows that a good etching rate and a stable in-plane distribution were obtained almost in the same manner as when the EP was mounted.

Example 3 It was evaluated whether EBEP can remove a fluorine-based organic substance having a thickness of about 15 nm on a glass substrate, which is difficult to detect in the final inspection step of the disk. EBEP TYPE II was used as a plasma device, and a prototype vacuum device was used as a vacuum device.

As the fluorinated oil, Z-DOL (manufactured by Ausimond) was used. This oil is a fluorinated compound similar to the fluorinated oil used as a lubricant for the movable part of the film forming apparatus previously identified as a substance causing organic contamination of the disk.

This fluorine-based oil was applied on the carbon protective film of the disk, and the film thickness was adjusted to 15 nm. FT-IR (model: 60 Mi) manufactured by Newly Instruments Co., Ltd. was used for measuring the film thickness of the fluorine-based oil. Two spectral positions of 880 and 1380 cm ^-1 were connected by a straight line, and using this as a background, a calibration curve was created from the absorption intensity, and the removal amount was evaluated from the thickness of the fluorine-based oil before and after the treatment.

The conditions of the EBEP process at the time of producing the evaluation sample are that the degree of vacuum of the process chamber 12 during discharge is 1 Pa and the discharge time in the process chamber 12 is 2 seconds. The gas concentration was adjusted by adding oxygen gas to argon gas.

FIG. 12 shows the current value of the cathode power supply 16 and the remaining amount of fluorine-based oil when the oxygen concentration is changed. The voltage value of the acceleration power supply 17 was set to 50V. This result indicates that the current value of the cathode power supply 16 is 2 A at any oxygen concentration.
As described above, it is shown that the fluorine-based oil having a thickness of 15 nm can be removed.

FIG. 13 shows the accelerating voltage value of the accelerating power supply 17 and the amount of fluorine-based oil removed when the oxygen concentration is changed. The current value of the cathode power supply 16 was 5 A. This result indicates that the voltage value of the accelerating power supply 17 is 20 V at any oxygen concentration.
As described above, it is shown that the fluorine-based oil having a thickness of 15 nm can be removed.

These results indicate that the present invention is extremely effective also as a method for cleaning a glass substrate.

<Example 4> Frequency of occurrence of late film peeling failure in a disk manufactured by mounting an EBEP in a vacuum apparatus of a mass production machine and performing an EBEP process on a glass substrate and a disk manufactured without performing the process. The differences were investigated.

When the EBEP process is performed, first,
The EBEP was mounted on the first station 20 of the mass production vacuum apparatus, and the film forming apparatus was mounted on the other stations. At this time, the film configuration and each film thickness were as follows: a soda lime-based glass substrate (model H1) manufactured by Nippon Sheet Glass Co., Ltd., a precoat film (CoCrZr alloy) of 22 nm, and a base film (Cr).
Ti alloy) 25 nm, magnetic film (CoCrPt alloy) 19
nm and a carbon protective film of 12 nm. The EBEP process conditions were as follows: a degree of vacuum of 1 Pa during discharge (oxygen concentration 70% by volume ratio, argon concentration 30% by volume ratio), a vacuum of about 10 ^-4 Pa during transport (transport time 2.2 seconds), and a discharge time of 2 seconds. Cathode power supply 16 voltage 50V, acceleration power supply 17 voltage 5A
And the process cycle is 9.0 seconds. Each of the disks created under these conditions was installed in a magnetic disk device at 10,000 units (the number of disks was 3 / unit), and the heads were randomly set to one.
A seek was performed for 00 hours. A similar random seek test was performed on a disc manufactured without performing the EBEP process.

The above test was used to compare the occurrence of defective peeling of the film with the disk device incorporating the disk subjected to the EBEP process and the disk device incorporating the disk not subjected to the EBEP process. When EBEP was not performed, this defect occurred in 97 out of 10,000 units, but when EBEP was performed, the defect occurred in 6 out of 10,000 units. This result indicates that the rate of occurrence of late peeling defects can be significantly reduced by introducing the EBEP process.

As described above, according to the present invention, the organic contaminants in the form of a glass substrate, which is a problem in the production of a thin film magnetic recording medium using a glass substrate, that is, a thin film magnetic disk using a glass substrate, are accompanied by an incidental problem. This shows that the method is extremely effective as a disk manufacturing method for efficiently removing a disk in a short cycle without any problems.

[0061]

As described above, the present invention provides the above EB
Introducing the EP process into the disk manufacturing process has the effect of reducing subsequent film peeling defects occurring in the magnetic disk device by 90% or more.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a process chamber pressure and a carbon protective film etching rate when a gas amount is constant.

FIG. 2 is a sectional view of a magnetic disk.

FIG. 3 shows the results of Auger observation of a subsequently peeled portion and a normal portion.

FIG. 4 is a process flow from cleaning of a magnetic disk to film formation.

FIG. 5 is a schematic diagram of an EBEP device.

FIG. 6 shows a relationship between a process chamber pressure and a carbon protective film etching rate at a constant gas exhaust conductance.

FIG. 7 shows a relationship between a radial position at 0.1, 1.0, and 4.0 Pa and an etching rate.

FIG. 8 shows a relationship between a radial position at 0.1, 1.0, and 4.0 Pa and an etching rate distribution.

FIG. 9 is a schematic diagram of a vacuum device of a mass production machine.

FIG. 10 shows a relationship between a radial position and an etching rate in a vacuum apparatus of a mass production machine.

FIG. 11 shows a relationship between a radial position and an etching rate distribution in a vacuum apparatus of a mass production machine.

FIG. 12 shows the relationship between the cathode current value and the remaining amount of fluorine-based oil.

FIG. 13 shows the relationship between the acceleration voltage value and the remaining amount of fluorine-based oil.

[Explanation of symbols]

1 glass substrate, 2 precoat film, 3 base film, 4
Magnetic film, 5 Protective film, 6 Lubricating film, 7 Cathode for plasma generation, 8 Argon gas inlet for source plasma, 9
S1 electrode, 10 S2 electrode, 11A electrode, 12 process chamber, 13 process gas inlet, 14
Disk, 15 vacuum exhaust port, 16 cathode power supply, 1
7 Acceleration power supply, 18 Conductance adjustment gate, 19
Load chamber, 20 first station, 21 mass production vacuum equipment main body, 22 unload chamber.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuo Yasuo 2880 Kozu, Odawara-shi, Kanagawa Prefecture F-term in the Storage Systems Division, Hitachi, Ltd. (Reference) 4K029 AA09 BD11 FA04 FA05 5D112 AA02 AA24 BA03 GA22

Claims (5)

[Claims] The present invention relates to a magnetic recording medium for continuously forming a thin film magnetic recording medium after irradiating a glass substrate with plasma of an argon-oxygen mixed gas at a pressure of 0.4 to 2.7 Pa by an electron beam excitation type plasma apparatus. Production method. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein said argon-oxygen mixed gas has an oxygen concentration of 10 to 70 volume percent. 3. The thin film magnetic recording medium according to claim 1, wherein a precoat film, an underlayer film, a magnetic film, and a protective film are continuously formed on a glass substrate. A method for manufacturing a magnetic recording medium. 4. A method for cleaning a glass substrate, wherein the glass substrate is irradiated with plasma by an electron beam excitation type plasma apparatus at a pressure of an argon oxygen mixed gas in a range of 0.4 to 2.7 Pa. 5. The glass substrate cleaning method according to claim 4, wherein the oxygen concentration of the argon oxygen mixed gas is from 10 to 70 volume percent.