JP2002001320A - Method of treating waste ozone water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent corrosion of a piping system and pollution of the environment caused by discharge of waste ozone water, when a high concentration of ozone water is used for a liquid phase ozone. SOLUTION: The waste ozone water 41 discharged from a substrate treating part 20 is introduced in to a reaction container 31, and is discharged to the outside of the system after it is irradiated with UV rays by an UV ray lamp 34. The waste ozone water 41 contains high concentration of dissolved ozone, substance for suppressing decomposition of ozone and a lot of organic matters produced in treatment of the substrate at the substrate treating part 20, but UV rays are efficiently utilized to obtain dissolved ozone without decomposing the organic matters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating waste ozone water after use in liquid ozone treatment with ozone water.

[0002]

2. Description of the Related Art In a process of manufacturing a semiconductor substrate or a glass substrate for a liquid crystal display device, a process of applying a resist, etching and removing the resist is repeated on the surface of the substrate. The resist stripping here is roughly classified into a wet process using a stripping solution or a mixed solution of sulfuric acid and hydrogen peroxide, and a dry process (ashing) using plasma, and each is used properly according to the purpose. When comparing the two, the wet treatment is more economical. This is because dry ashing by plasma requires a vacuum or the like.

However, wet processing using a stripping solution or a mixture of sulfuric acid and hydrogen peroxide has a great environmental problem since the stripping solution and the mixture of sulfuric acid and hydrogen peroxide are generally environmental pollutants. For this reason, the development of clean and economical alternative methods that have no environmental problems is being promoted, and one of these methods is considered as a peeling treatment using ozone.

As is well known, ozone has a strong oxidizing power and is decomposed into oxygen, so there is no concern about environmental pollution, and there is no problem with exhaust gas and wastewater treatment. It is attracting attention as an oxidative decomposition agent.

[0005] The substrate processing using ozone is roughly classified into a gas phase processing and a liquid phase processing. In the gas phase treatment, the substrate surface is treated with ozone gas containing ozone. On the other hand, the liquid phase treatment is a treatment of the substrate surface with ozone water in which ozone is dissolved, and is classified into a batch type and a single-wafer type according to the number of processed substrates. In addition, it can be divided into dip treatment and running water treatment according to the contact state of the substrate and ozone water,
Dip processing is often combined with batch processing, and running water processing is often combined with single wafer processing.

Comparing the gas phase ozone treatment and the liquid phase ozone treatment, in the case of the gas phase treatment called ashing, it is necessary to heat the substrate to a high temperature of 200 to 300 ° C. in order to increase the reaction rate, which increases the heating cost. In addition, the substrate may be damaged by the heating. In addition, since the rate is lower than that of oxygen plasma ashing, ultraviolet rays may be used in some cases. In such a case, there is a concern about damage due to irradiation with ultraviolet rays.

On the other hand, in the case of the liquid phase ozone treatment, the high temperature heating of the ozone water is impossible, so that the problem caused by the heating does not occur, but the essential problem is that the reaction rate is extremely low. There is. For this reason, the liquid phase treatment using ozone water has not yet been put to practical use in resist stripping, and is currently put to practical use only at the level of cleaning the substrate.

[0008]

By the way, the dissolved ozone concentration of ozone water used for liquid phase ozone treatment such as substrate washing has hitherto been at most about 10 mg / L.
In this case, the dissolved ozone concentration of the waste ozone water after use in the liquid phase ozone treatment is low, and the decomposition of ozone continues after use, so that the waste ozone water can be directly discharged from the processing apparatus. There was no problem. Rather, it was considered that there was no need for post-treatment of the waste ozone water as one of the advantages of the liquid-phase ozone treatment, and it was natural that no post-treatment was performed.

However, in order to improve the low reaction rate which is an obstacle in applying the liquid phase ozone treatment to resist stripping, it is necessary to increase the concentration of dissolved ozone in ozone water. Such problems have become apparent.

[0010] The present applicant has previously reported that 200 gO ₃ / Nm ³
As described above, a high-performance ozonizer capable of stably generating a high-concentration ozone gas of 300 gO ₃ / Nm ³ or more has been developed. By combining high-concentration ozone gas generated by this high-performance ozonizer with pressurization, 50 m
High-concentration ozone water of not less than g / L, and more preferably not less than 100 mg / L can be generated. Also, ozone in a liquid is not as good as ozone in a gas, but decomposes over time, so it is important to maintain its high concentration until use. To maintain this, it is effective to add a substance such as acetic acid that suppresses the decomposition of ozone in the liquid.

High-concentration ozone water to which an ozone decomposition inhibitor such as acetic acid has been added exhibits a high reaction rate when applied to liquid phase ozone treatment such as resist stripping. But on the other hand,
The waste ozone water used for the liquid phase ozone treatment has an extremely high ozone concentration and cannot be expected to decompose ozone over time. It has been found that conventional liquid-phase ozone treatment with a clean image causes unexpected problems such as early corrosion and environmental pollution.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ozone water discharge system capable of preventing corrosion of piping systems and environmental pollution caused by discharge of ozone water when high-concentration ozone water is used for liquid phase ozone treatment. It is to provide a processing method.

[0013]

SUMMARY OF THE INVENTION The treatment of waste ozone water, which occurs when high-concentration ozone water is used for liquid-phase ozone treatment, that is, the treatment of removing dissolved ozone in waste ozone water, is unexpectedly troublesome. This is because not only the dissolved ozone concentration is high, but also the decomposition of dissolved ozone is suppressed by acetic acid and the like, and a large amount of organic substances such as resist decomposed substances generated in the liquid phase ozone treatment are present to decompose dissolved ozone. This is because there is a high risk that measures for the above will be used preferentially for the decomposition of this organic matter.

[0014] Under such circumstances, the present inventors have studied various methods for efficiently decomposing dissolved ozone in waste ozone water. As a result, they found that irradiation with ultraviolet rays was effective.

The method of treating waste ozone water of the present invention has been developed based on such knowledge, and irradiates ultraviolet light to waste ozone water after use in liquid-phase ozone treatment with ozone water in which ozone is dissolved. There is a feature in the point.

The liquid phase ozone treatment is typically a treatment for removing organic substances from the substrate with ozone water, but may also include the formation of an oxide film on a substrate.

The process of removing organic substances from the substrate with ozone water is typically a process of removing fine particles, but a resist stripping process and the like can also be used.

The method for treating waste ozone water according to the present invention is characterized in that even for high-concentration waste ozone water containing dissolved ozone of 20 mg / L or more, or even 100 mg / L or more, the dissolved ozone concentration is discharged to a normal drainage facility. Can be reduced to 10 mg / L or less, which does not adversely affect the piping and the like.
In addition, the waste ozone water contains 5 mg / m of an ozone decomposition inhibitor.
L or more, the dissolved ozone concentration should be 10 m
g / L or less. Furthermore, even when the waste ozone water contains an organic substance as a TOC value of 100 mg / L or more, the dissolved ozone concentration can be reduced to 10 mg / L or less.

The ozone decomposition inhibitor is typically acetic acid, but may also include carbonic acid, phosphoric acid, carboxylic acid and the like.

The ultraviolet light for irradiating the waste ozone water is radiated by an ultraviolet lamp, and its wavelength is effective for ozone decomposition.
Those containing 54 nm, particularly those containing a large amount of 254 nm, are preferred. Specifically, those irradiated from a low-pressure mercury lamp, excimer lamp or the like are preferred. Ultraviolet light also preferably has a high output from the viewpoint of the decomposition efficiency of dissolved ozone. Specifically, in the case of a low-pressure mercury lamp, the power per lamp is 100%.
It is preferable that the UV３０C conversion efficiency is 30% or more at W or more and the UV─C emission density is 0.5 W / cm or more.

In order to adjust the pH to less than 7, the waste ozone water may be added with an acid such as hydrochloric acid, sulfuric acid or hydrofluoric acid in an amount of 5 mg / L or more. In order to adjust the pH to 7 or more, an alkali such as sodium hydroxide, potassium hydroxide, or ammonia may be added at 5 mg / L or more.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an apparatus configuration diagram showing an example of a substrate processing apparatus using the method for treating waste ozone water of the present invention.

The substrate processing apparatus removes a resist from a semiconductor substrate 10 called a wafer. The substrate processing apparatus includes a substrate processing unit 20 and a waste ozone water processing unit 30.

The substrate processing unit 20 uses the rotor 21 to
Is supplied to the center of rotation of the substrate 10 from the nozzle 22 above. The ozone water 40 supplied on the center of rotation of the substrate 10 spreads on the surface of the substrate 10 to the outer peripheral side by centrifugal force, and decomposes and removes the resist applied on the surface.

The ozone water 40 contains, for example, 100 mg / L or more of dissolved ozone to increase the reaction rate, and contains, for example, 100 mg / L or more of acetic acid for suppressing the decomposition of the ozone.

The drained ozone water 41 used after stripping the resist flows down from the substrate 10 to the lower receiving portion 23, is collected, and is sent to the drained ozone water processing unit 30.

The waste ozone water treatment section 30 is provided with a waste ozone water 41.
, A UV lamp 34 for irradiating the treated water in the reaction vessel 31 with ultraviolet light, and a power supply unit 35 for supplying electric power to the ultraviolet lamp 34. The ultraviolet lamp 34 is, for example, a low-pressure mercury lamp housed in a quartz tube 33 inserted into the reaction vessel 31. The power supply unit 35 supplies power to the ultraviolet lamp 34 through the connectors 36 and 37. A rectifying plate 32 is provided in the reaction vessel 31 to generate turbulence in the treated water and perform stirring.

The waste ozone water 41 sent from the substrate processing section 20 contains an ozone decomposition suppressing substance, and maintains a high dissolved ozone concentration equivalent to that during substrate processing. In addition, it contains a large amount of resist decomposing substances accompanying the resist stripping. However, this waste ozone water 41 is also used in the reaction vessel 3
By irradiating with ultraviolet light having a wavelength of 254 nm in the inside 1, high-concentration dissolved ozone is efficiently and selectively decomposed, and becomes a mere organic matter-containing wastewater containing substantially no dissolved ozone and out of the reaction vessel 31. Is discharged.

Therefore, there is no concern that the drainage system of the substrate processing apparatus will be corroded. There is no danger of environmental pollution. In addition,
When the organic matter contained in the wastewater becomes a problem, the wastewater may be removed appropriately by a known method.

[0030]

Next, an embodiment of the present invention will be described.

Ultraviolet light was irradiated in the reaction vessel to experimental ozone water, which assumed waste ozone water having a dissolved ozone concentration of about 100 ppm. For UV irradiation, use a UV lamp (low-pressure mercury lamp) with a power consumption of 160 W and a UV output of 59 W for 1-4.
Used this book. The flow rate of the ozone water is 4.5 L / min, and the residence time of the ozone water in the reaction vessel is 3.3 minutes.

Table 1 shows the results of measuring the dissolved ozone concentration at the inlet and outlet of the reaction vessel. As can be seen from Table 2,
100pp by using two UV lamps (320W)
m can be almost completely decomposed and removed.

[0033]

[Table 1]

Table 2 shows the results when 100 mg / L of acetic acid was added to the above ozone water. Even if acetic acid which is an ozone decomposition inhibitor is added, three UV lamps are used (48
0W), it is possible to almost completely decompose and remove 100 mg / L of dissolved ozone.

[0035]

[Table 2]

Assuming a condition where a large amount of organic substances including an ozone decomposition inhibiting substance is present, acetic acid is added to the above ozone water in an amount of 10%.
00 mg / L was added. The water quality at this time is 480 mg / L as a TOC value which is an index of the amount of organic matter. Table 3 shows the processing results. Even if the TOC value is 480 mg / L,
100mg by using 4 UV lamps (640W)
/ L of dissolved ozone can be almost completely decomposed and removed.
In the case of using four UV lamps (640 W), the TOC value after the ultraviolet irradiation treatment was about 430 mg / L. This is because ultraviolet light is not used much for the decomposition of organic matter,
This is considered to be evidence that it is more effectively used for ozonolysis.

[0037]

[Table 3]

Assuming that the pH is less than 7, the pH is adjusted to 3.8 by adding acetic acid to ozone water;
Table 4 shows the results when the pH was adjusted to 8.2 by adding ammonium bicarbonate to ozone water on the assumption that the pH was 7 or more. The ozone can be decomposed and removed regardless of whether the treated water is acidic or alkaline.

[0039]

[Table 4]

The reason why high-concentration dissolved ozone is effectively decomposed by ultraviolet irradiation even in the presence of a large amount of an organic substance containing an ozone decomposition inhibitor is considered as follows.

Ozone is decomposed by light having a wavelength of 254 nm among ultraviolet rays. On the other hand, the light absorption of the organic substance is not around 254 nm. Thus, ozone decomposition is not affected by the presence of organic matter. FIG. 2A shows ozone water (11).
(mg / L) around 250 nm.
FIG. 2B shows acetic acid (60000 m) as an example of an organic substance.
(g / L) around 250 nm. As can be seen from FIG. 2, since the absorption of light by the organic substance is not near 254 nm, even in the presence of a large amount of organic substance, high-concentration dissolved ozone is efficiently and selectively decomposed by ultraviolet irradiation. From this viewpoint, it is preferable that the ultraviolet ray contains a large amount of light having a wavelength of 254 nm.

[0042]

As described above, the method of treating waste ozone water according to the present invention efficiently removes ozone that is dissolved in a large amount in waste ozone water even under the condition that a large amount of organic matter containing an ozone decomposition inhibitor is present. Can be decomposed and removed. Therefore, when high-concentration ozone water is used for the liquid-phase ozone treatment, it is possible to prevent the corrosion of the piping system and environmental pollution caused by the discharge of the waste ozone water, and the efficient liquid phase This has the effect of enabling ozone treatment.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing an example of a substrate processing apparatus using a method of treating waste ozone water of the present invention.

FIG. 2 is a graph showing light absorption of ozone and organic substances.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Substrate 20 Substrate processing part 30 Waste ozone water processing part 31 Reaction container 34 Ultraviolet lamp 40 Ozone water 41 Exhausted ozone water

Continued on the front page F term (reference) 2H096 AA25 AA27 LA02 4D037 AA11 AB11 BA18 BB01 BB09 CA14 5F046 MA02 MA05

Claims (7)

[Claims] 1. A method for treating waste ozone water, comprising irradiating ultraviolet light to waste ozone water after use in liquid-phase ozone treatment with ozone water in which ozone is dissolved. 2. The method for treating waste ozone water according to claim 1, wherein the liquid phase ozone treatment is a treatment for removing organic substances from the substrate with ozone water. 3. The method for treating waste ozone water according to claim 2, wherein the treatment for removing organic substances from the substrate with ozone water is a resist stripping treatment. 4. The method according to claim 1, wherein the discharged ozone water contains at least 20 mg / L of dissolved ozone at the stage of irradiation with ultraviolet rays. 5. The method for treating waste ozone water according to claim 4, wherein the concentration of dissolved ozone in the waste ozone water is reduced to 10 mg / L or less by ultraviolet irradiation. 6. The method according to claim 1, wherein the waste ozone water contains at least 5 mg / L of a substance that suppresses the decomposition of ozone. 7. The method for treating waste ozone water according to claim 1, wherein the waste ozone water contains an organic substance at a TOC value of 100 mg / L or more.