JP2001070898A - Cleaning liquid and cleaning method for precision substrates - Google Patents

Abstract

(57) [Problem] To provide a cleaning liquid and a cleaning method capable of preventing particles once separated from a substrate from being re-adhered by cleaning without lowering the cleaning performance when cleaning a precision substrate. SOLUTION: The cleaning liquid for cleaning a precision substrate is an aqueous solution containing an alkaline surfactant prepared by diluting an alkaline surfactant with diluting water to adjust the oxidation-reduction potential to −300 mV or less. A cleaning liquid and a cleaning method for a precision substrate which is hydrogen water in which hydrogen is dissolved at 1 ppm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a quartz glass substrate,
The present invention relates to a cleaning liquid and a cleaning method for cleaning a precision substrate made of quartz glass such as a mask blank substrate, a photomask substrate, and a liquid crystal glass substrate.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of the size of VLSI, the demand for cleaning a photomask substrate used as an exposure substrate has been increasing. The photomask substrate is formed by depositing a metal thin film of chromium or the like on a quartz glass substrate by vapor deposition or sputtering to form a mask blank substrate, applying a resist or the like to the substrate, exposing it to light, etching, and forming a pattern on the surface. Therefore, in order to obtain a clean photomask substrate, a substrate that has been cleaned from the stage of a quartz glass substrate and a mask blanks substrate is required. The liquid crystal glass substrate is also required to have a high degree of cleanliness as with the photomask substrate.

To realize cleaning, it is necessary to remove contaminants. For this purpose, a cleaning method includes immersion cleaning in which a substrate is immersed in an immersion tank containing a cleaning liquid, and a shower in which the cleaning liquid is poured by a shower or the like. There are a ring method, a scrub cleaning method using a sponge, and the like, and a method combining them is widely used. At that time, a method of increasing the cleaning efficiency by applying ultrasonic waves is also widely used.

[0004] By the way, in order to remove particles, especially inorganic substances, ammonia peroxide (ammonia + hydrogen peroxide solution) and alkaline surfactants have been used. Although the cleaning effect of ammonia peroxide is high, it dissolves the substrate surface, albeit in a small amount, and may cause surface roughness,
Flatness may be impaired. For this reason, under the current situation where the demand for higher precision and higher density is strict, there is a problem in the future use of ammonia peroxide, which is apt to deteriorate in quality. Further, there are many problems in using the cleaning liquid in consideration of the concentration change of the cleaning liquid, cost, waste liquid treatment, exhaustion, safety and the like.

[0005] As an alternative, there is a method using an alkaline surfactant. However, with the recent refinement and high density of devices, submicron design rules have been adopted.
Insufficient cleaning only with the cleaning ability of the current cleaning agent,
Poor yield. Further, even if the cleaning agent has excellent cleaning ability, there is a disadvantage that particles cannot be completely removed because a part of the removed impurities adhere to the substrate again. In order to improve the cleaning ability, increase the replacement ratio of the cleaning agent in immersion cleaning, increase the concentration of the cleaning agent,
There are various countermeasures such as increasing the frequency of the ultrasonic wave, but none of them has achieved satisfactory abilities. In addition, this method is not a practical method in consideration of cost, waste liquid treatment, and the like.

Recently, it has been proposed that what is called functional water is effective for cleaning. Hydrogen water or cathode water is used for particle removal. The effect of the hydrogen water is to make the zeta potential of the substrate surface and particles negative or even more negative since the oxidation-reduction potential is negative. Furthermore, by using the application of ultrasonic waves in combination with the cleaning effect of ultrasonic waves and hydrogen water,
Both the particles separated from the substrate surface and the substrate surface have a negative zeta potential, so they repel electrically and help to prevent re-adhesion.

[0007] Since the hydrogen water itself has a cleaning effect but is low, a method of further increasing the cleaning ability by adding ammonia has been performed. However, even with this ammonia-added hydrogen water, the cleaning effect is lower than the cleaning effect of the alkaline surfactant, so that it cannot be used for a state-of-the-art substrate requiring high precision. In addition, it has been pointed out that alkaline surfactants may be changed to environmental hormones and biodegradability.
Furthermore, since there is no particle-free surfactant as a ready-made product, if the concentration is high, the cleaning effect is high, but there is a problem in that foreign substances are contaminated by the cleaning agent itself.

[0008] There is also a method of increasing the detergency by using ultrasonic waves in combination. Again, the higher the frequency, the higher the cleaning effect, but it requires more power, which is not realistic in terms of cost from a manufacturing standpoint. Further, when an ultrasonic wave having a too high frequency is applied, there is a concern that the substrate to be cleaned may be damaged.

[0009]

As described above, when removing particles, it is necessary to obtain a substrate having no particles adhered to the substrate surface after cleaning.
Therefore, even if the particles are cleaned and removed using a cleaning agent having a high cleaning ability, if the particles adhere again after the cleaning, the cleaning may be insufficient. Therefore, it is necessary to take measures to prevent the particles separated from the substrate from being reattached by the cleaning without lowering the cleaning ability.

In view of the above, the present invention has been made in view of the above-described problems. In cleaning a precision substrate, particles which once separated from the substrate surface by cleaning are not re-attached without lowering the cleaning performance. A main object of the present invention is to provide a cleaning solution and a cleaning method capable of preventing the above.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, a cleaning liquid for a precision substrate according to the present invention is a cleaning liquid for cleaning a precision substrate, and is obtained by diluting an alkaline surfactant with diluting water to obtain a redox potential. Is an aqueous solution containing an alkaline surfactant prepared to be -300 mV or less.

According to the cleaning liquid for a precision substrate having the above-described structure, it is possible to prevent the particles which have separated from the substrate surface from being re-attached by the cleaning without lowering the inherent cleaning ability of the alkaline surfactant. A cleaned precision substrate can be easily obtained.

In this case, it is preferable that the dilution water is hydrogen water in which 1 ppm or more of hydrogen is dissolved. As described above, when the dilution water is hydrogen water in which hydrogen is dissolved at 1 ppm or more, the cleaning ability of the hydrogen water itself is weak, but the cleaning ability of the cleaning solution containing the alkaline surfactant diluted with the hydrogen water is both. It is high enough by the synergistic effect. Further, since the oxidation-reduction potential of the hydrogen water can be adjusted to −300 mV or less, the zeta potential of the substrate surface and the particles becomes negative, and the particles repel each other electrically to prevent the particles from re-adhering to the substrate. Becomes possible.

Further, in this case, the concentration of the alkaline surfactant can be set to 0.05% or less. Usually, in precision cleaning, 0.3 to 5% is used. Although the cleaning ability of the alkaline surfactant is higher when the concentration is higher, the cleaning ability of the cleaning liquid of the present invention hardly decreases even at a low concentration of 0.05% or less due to a synergistic effect with hydrogen water. , Cleaning can be achieved. Therefore, the load on the environment can be reduced as compared with the conventional cleaning agent, and the cleaning cost can be improved.

Here, the method for cleaning a precision substrate of the present invention is a method for cleaning a precision substrate using the above-described cleaning liquid of the present invention. As described above, the use of the cleaning solution of the present invention enables efficient cleaning of a precision substrate, and further prevents particles that have left the substrate surface from being re-adhered to the cleaning, and as a result, a high degree of cleaning can be achieved. A precision substrate can be easily obtained.

The method for cleaning a precision substrate according to the present invention is a method for cleaning a precision substrate by a wet method, wherein the alkaline surfactant is diluted with hydrogen water to reduce the oxidation-reduction potential to -30.
The method is characterized in that the precision substrate is adjusted to 0 mV or less, and the precision substrate is washed using a washing solution containing the alkaline surfactant.

According to such a method, the excellent cleaning ability of the alkaline surfactant and the ability of the hydrogen water to prevent the particles from re-adhering to the substrate due to the negative oxidation-reduction potential act effectively. Highly precise substrates can be cleaned. Therefore, it is possible to improve the productivity and the yield, and also to improve the quality and the cost.

In this case, it is preferable to apply ultrasonic waves to the cleaning liquid to clean the precision substrate. Typically 0.8 for cleaning
Although using high frequency ultrasound exceeding MHz,
When washing with the washing solution of the present invention, the washing solution is 0.8 MH.
0.8M only by applying low frequency ultrasonic wave below z
A high cleaning effect substantially equal to or higher than Hz can be obtained, the power cost can be reduced, and the substrate to be cleaned is not damaged.

In this case, the precision substrates to be cleaned can be a quartz glass substrate, a mask blank substrate, a photomask substrate, and a liquid crystal glass substrate. The cleaning liquid and the cleaning method of the present invention act extremely effectively on these precision substrates, exhibit high cleaning performance, and can prevent particles that once separated from the substrate surface from being re-attached during cleaning, and A purified precision substrate can be obtained. Further, they are chemically stable, and do not corrode these precision substrates and do not become a contamination source by being adsorbed on the substrate surface.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited thereto. The present inventors have investigated and studied a cleaning liquid and a cleaning method in order to cope with a high demand for cleaning a so-called precision substrate such as a quartz glass substrate, a mask blank substrate, a photomask substrate, and a liquid crystal glass substrate. The present inventors have found that a cleaning solution obtained by diluting an alkaline surfactant with hydrogen water has an extremely high cleaning ability and is particularly effective in preventing reattachment of particles, and has completed the present invention by observing various conditions.

That is, as described above, the alkaline surfactant has a higher cleaning ability than the ammonia-added hydrogen water as described above, but has a problem of reattachment of particles. This is problematic for the water to dilute. Normally, ultrapure water is used as the dilution water, and the oxidation-reduction potential is positive and is usually about +600 mV. Therefore, even if the alkaline surfactant is diluted with ultrapure water, since the oxidation-reduction potential is usually positive, the zeta potential of the particles is not negative or slightly negative, and thus the particles are separated from the substrate surface by washing. Particles may reattach. Therefore, it was considered that even if the cleaning ability was high, the particles could not be completely removed as a result.

Therefore, the cleaning solution for precision substrates according to the present invention is a cleaning solution for cleaning precision substrates, wherein an alkaline surfactant is diluted with diluting water to reduce the oxidation-reduction potential to -300 m.
V or less. By doing this,
The zeta potential between the substrate surface and the particles can be made negative, and the particles can be electrically repelled from each other to prevent the particles from re-adhering to the substrate.

Here, the alkaline surfactant is a so-called cationic surfactant, and is commercially available as NCW-
LC-3 (trade name, manufactured by Wako Pure Chemical Industries, Ltd.), Semiclean L
C-2EL (trade name, manufactured by Yokohama Yushi Kogyo KK) and the like.

As the dilution water of the alkaline surfactant,
Hydrogen water in which hydrogen is dissolved in an amount of 1 ppm or more is preferable. As described above, if the dilution water is hydrogen water in which hydrogen is dissolved at 1 ppm or more, the cleaning ability of the cleaning liquid itself is weak, but the cleaning ability of the cleaning liquid containing the alkaline surfactant diluted with the hydrogen water is synergistic. The effect is high enough. Further, the oxidation-reduction potential of the hydrogen water is determined by the hydrogen concentration.
It can be easily adjusted to 300 mV or less.

In this case, the concentration of the alkaline surfactant can be reduced to 0.05% or less. In general, the cleaning ability of the alkaline surfactant is higher when the concentration is higher, but in the case of the cleaning liquid of the present invention, the cleaning ability is almost not increased even at a low concentration of 0.05% or less due to a synergistic effect with hydrogen water. Without lowering, cleaning can be achieved. Therefore, as compared with the conventional high-concentration method, the burden on the environment can be further reduced, and the cleaning cost can be improved.

As explained above, the cleaning solution of the present invention
In the cleaning of precision substrates and the like, the cleaning ability is high, and the ability to prevent reattachment of particles and the like is excellent. Therefore, according to the cleaning method using the cleaning liquid of the present invention, a precision substrate can be efficiently cleaned, and a highly purified precision substrate can be easily obtained.

In the cleaning method of the present invention, it is preferable to clean the precision substrate by applying ultrasonic waves to the cleaning liquid. Usually, high-frequency ultrasonic waves exceeding 0.8 MHz were used, but when cleaning with the cleaning liquid of the present invention, a sufficiently high cleaning effect can be obtained only by applying ultrasonic waves of 0.8 MHz or less to the cleaning liquid. Power costs can be reduced.

In applying the cleaning solution and cleaning method of the present invention, the precision substrate to be cleaned can be a quartz glass substrate, a mask blank substrate, a photomask substrate, or a liquid crystal glass substrate. The cleaning liquid and the cleaning method of the present invention act extremely effectively on these precision substrates to exhibit high cleaning performance, and can prevent particles that once separated from the substrate surface from being re-attached in the cleaning. A purified precision substrate can be obtained. Further, the cleaning liquid of the present invention is chemically stable, and does not corrode these precision substrates and does not become a source of contamination by being adsorbed on the substrate surface. Therefore, the cleaning liquid and the cleaning method of the present invention are extremely suitable for cleaning the above-mentioned precision substrate, which requires higher precision.

As a method for cleaning a precision substrate using the cleaning liquid of the present invention, a conventionally known immersion cleaning method in which a substrate is immersed in an immersion tank containing the cleaning liquid, a showering method in which the cleaning liquid is poured by a shower or the like, There is a scrub cleaning method using a sponge or the like, and further a method combining them, and the like, and in that case, a method using ultrasonic waves in combination is also effective. That is, the cleaning method of the present invention is not particularly limited in its cleaning method, and can be applied to any method.

[0030]

EXAMPLES The present invention will now be described specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. Example 1 [Cleaning Effect on Photomask Blanks Substrate] A solution of silica powder (SiO ₂ ) suspended in ultrapure water (1 g /
L), a 6-inch square photomask blank substrate provided with a CrON film was immersed for 30 seconds to prepare a contaminated substrate.

The contaminated substrate was placed in a dipping tank A at 1.2M.
The substrate was immersed in a cleaning solution to which ultrasonic waves of Hz were applied for 5 minutes for cleaning. At this time, the cleaning liquid is N, which is an alkaline surfactant.
CW-LC-3 (trade name, manufactured by Wako Pure Chemical Industries, Ltd.) was diluted with hydrogen water having a hydrogen concentration of 1 ppm or more and an oxidation-reduction potential of -736 mV as diluting water to reduce the surfactant concentration to 0.3%. It was prepared. Then, the cleaning liquid was introduced from the bottom of the immersion tank A, and the contaminated substrate was cleaned while overflowing from the top.

Next, the substrate was immersed in an immersion tank B for 5 minutes by flowing ultrapure water and applying ultrasonic waves of 1 MHz.
I rinsed. Next, the substrate was further transferred to the immersion tank C, and the substrate was immersed and rinsed under the same conditions as those of the immersion tank B.
Next, after spin drying, the number of particles on the substrate surface was measured with a light collecting lamp of 400,000 lux. As a result, the number of particles that existed at least 10,000 particles / substrate before the cleaning is drastically reduced to 3 particles / substrate. The washing conditions and results are summarized in Table 1.

(Example 2) Semi-clean LC-2EL (trade name, manufactured by Yokohama Yushi Kogyo Co., Ltd.) was used as the alkaline surfactant.
The washing was carried out under the same conditions as in Example 1 except for using. The hydrogen water used as the dilution water had a hydrogen concentration of 1 ppm or more and an oxidation-reduction potential of −753 mV. The washing conditions and the results are summarized in Table 1 and also described.

(Comparative Example 1) Washing was carried out under the same conditions as in Example 1 except that ultrapure water was used as dilution water for the alkaline surfactant. The oxidation-reduction potential of ultrapure water was +276 mV. The washing conditions and the results are summarized in Table 1 and also described.

(Comparative Example 2) Washing was carried out under the same conditions as in Example 2 except that ultrapure water was used as dilution water for the alkaline surfactant. The washing conditions and the results are summarized in Table 1 and also described.

[0036]

[Table 1]

From Table 1, it can be seen that the washing ability is sufficient regardless of the type of the alkaline surfactant, and that hydrogen water is extremely effective as the dilution water.

Example 3 Washing was carried out under the same conditions as in Example 1 except that the concentration of the alkaline surfactant was changed to 0.03%. The washing conditions and results are summarized in Table 2.

(Embodiment 4) The frequency of the ultrasonic wave is set to 0.4 MHz.
Washing was carried out under the same conditions as in Example 1 except that z was used. The washing conditions and results are summarized in Table 2 and also described.

Example 5 Washing was performed under the same conditions as in Example 1 except that the concentration of the alkaline surfactant was 0.03% and the frequency of the ultrasonic wave was 0.4 MHz. The washing conditions and results are summarized in Table 2 and also described.

[0041]

[Table 2]

From Table 2, it can be seen that even if the concentration of the alkaline surfactant is low, the frequency of the ultrasonic wave is low, and even if the concentration of the alkaline surfactant is low and the dilution water is hydrogen water, It can be seen that the washing ability is higher than the dilution with ultrapure water.

Example 6 [Cleaning Effect on Quartz Glass Substrate] A solution of silica powder (SiO ₂ ) suspended in ultrapure water (1 g /
In L), a 6-inch square quartz glass substrate was immersed for 30 seconds to prepare a contaminated substrate. The contaminated substrate was immersed in a cleaning liquid to which 1.2 MHz ultrasonic wave was applied in an immersion tank A for 5 minutes to be cleaned. At this time, NCW-LC-3 (trade name, manufactured by Wako Pure Chemical Industries, Ltd.), which is an alkaline surfactant, was used as a washing solution with a hydrogen concentration of 1 ppm or more and an oxidation-reduction potential of -7.
The diluted water was diluted with 36 mV hydrogen water until the surfactant concentration became 0.3%. Then, the cleaning liquid was introduced from the bottom of the immersion tank A, and the contaminated substrate was cleaned while overflowing from the top.

Next, the substrate was immersed in an immersion tank B by immersing it in ultrapure water and applying ultrasonic waves of 1 MHz for 5 minutes to rinse it. Next, the substrate was further transferred to the immersion tank C, and the substrate was immersed and rinsed under the same conditions as those of the immersion tank B. Next, after spin drying, the number of particles on the substrate surface was measured with a light collecting lamp of 400,000 lux. As a result, 7 or more particles / substrate before cleaning were found.
The number of products / substrate has dropped sharply. Table 3 summarizes the washing conditions and results.

Example 7 Semi-clean LC-2EL (trade name, manufactured by Yokohama Yushi Kogyo Co., Ltd.) was used as an alkaline surfactant.
Washing was carried out under the same conditions as in Example 6 except for using. The hydrogen water used as the dilution water had a hydrogen concentration of 1 ppm or more and an oxidation-reduction potential of −753 mV. The washing conditions and the results are summarized in Table 3 and also described.

(Comparative Example 3) Washing was carried out under the same conditions as in Example 6 except that ultrapure water was used as dilution water for the alkaline surfactant. The washing conditions and the results are summarized in Table 3 and also described.

(Comparative Example 4) Washing was carried out under the same conditions as in Example 7 except that ultrapure water was used as dilution water for the alkaline surfactant. The washing conditions and the results are summarized in Table 3 and also described.

[0048]

[Table 3]

From Table 3, it can be seen that the alkaline surfactant has a high cleaning ability irrespective of the type, and hydrogen water is suitable for the dilution water.

Example 8 Washing was performed under the same conditions as in Example 6 except that the concentration of the alkaline surfactant was changed to 0.03%. The washing conditions and results are summarized in Table 4.

(Embodiment 9) The frequency of the ultrasonic wave is set to 0.4 MHz.
Washing was carried out under the same conditions as in Example 6, except that z was used. The washing conditions and the results are summarized in Table 4 and shown together.

Example 10 Washing was performed under the same conditions as in Example 6 except that the concentration of the alkaline surfactant was 0.03% and the frequency of the ultrasonic wave was 0.4 MHz. The washing conditions and the results are summarized in Table 4 and shown together.

[0053]

[Table 4]

From Table 4, it can be seen that even if the concentration of the alkaline surfactant is low, the frequency of the ultrasonic wave is low, and even if the concentration and the frequency are low, if the dilution water is hydrogen water, It can be seen that the washing ability is higher than the dilution with ultrapure water.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

[0056]

As described above, if the precision substrate is cleaned using the cleaning solution obtained by diluting the alkaline surfactant of the present invention with hydrogen water, inorganic substances and particles on the substrate surface are greatly reduced, and the substrate is stably formed. In addition, a substrate surface with extremely high cleanliness can be formed, and productivity and yield can be improved. Further, the concentration of the cleaning liquid and the frequency of the ultrasonic wave applied to the cleaning liquid can be reduced, and the cost can be improved.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masayuki Nakatsu 28, Nishifukushima, Nishifukushima-mura, Nakakushiro-gun, Niigata Pref. (28) Inventor Yukio Shibano 28-28 Nishifukushima, Kushiro-son, Nakakushiro-gun, Niigata Pref. Shin-Etsu Chemical Co., Ltd. F-term in the laboratory (reference) 3B201 AA01 AA03 AB01 BB04 BB83 BB92 BB94 CB15 CC01 CC13 CC21

Claims (8)

[Claims] 1. A cleaning liquid for cleaning a precision substrate, wherein the cleaning liquid is an aqueous solution containing an alkaline surfactant prepared by diluting an alkaline surfactant with diluting water to adjust the oxidation-reduction potential to −300 mV or less. Cleaning liquid for precision substrates. 2. The cleaning liquid for precision substrates according to claim 1, wherein the dilution water is hydrogen water in which hydrogen is dissolved at 1 ppm or more. 3. The method according to claim 1, wherein the concentration of the alkaline surfactant is 0.1.
The cleaning liquid for precision substrates according to claim 1 or 2, wherein the cleaning liquid is at most 05%. 4. A method for cleaning a precision substrate using the cleaning liquid according to claim 1. 5. A method of cleaning a precision substrate by a wet method, wherein an alkaline surfactant is diluted with hydrogen water to adjust an oxidation-reduction potential to −300 mV or less, and a cleaning liquid containing the alkaline surfactant is used for precision cleaning. A method for cleaning a precision substrate, comprising cleaning the substrate. 6. The method for cleaning a precision substrate according to claim 4, wherein ultrasonic waves are applied to the cleaning liquid to clean the precision substrate. 7. The method for cleaning a precision substrate according to claim 6, wherein the frequency of the ultrasonic wave applied to the cleaning liquid is 0.8 MHz or less. 8. The precision substrate according to claim 4, wherein the precision substrate to be cleaned is a quartz glass substrate, a mask blank substrate, a photomask substrate, and a liquid crystal glass substrate. Substrate cleaning method.