KR20020049217A - Manufacturing method of ultrapure water - Google Patents

Abstract

PURPOSE: A method of manufacturing ultrapure water by using acid-treated activated carbon in the first step of manufacturing is provided to prevent increasing of TOC which is occurred when pH is increased of disposed water as change of activated carbon. CONSTITUTION: In manufacturing of ultrapure water, acid-treated activated carbon or ordinary activated carbon rinsed with acid water needs at the first step of manufacturing. The pH of acid-treated activated carbon is 3-7. The acid water that rinses activated carbon is made by mixing withdrawal water and raw water.

Description

Manufacturing method of ultrapure water {Manufacturing method of ultrapure water}

The present invention relates to a method of producing ultrapure water, and more particularly, to first convert activated carbon in the preparation of ultrapure water through preliminary treatment of raw water and through a first pure water production step and a second pure water production step including activated carbon and ion exchange resin. The present invention relates to a method of producing ultrapure water capable of suppressing an increase in total organic carbon concentration due to a rise in pH generated at the time.

Ultrapure water, which is used in semiconductor manufacturing plants, is becoming more stringent as the microstructure of semiconductor devices develops. Especially in factories that manufacture semiconductor devices with integrated densities of more than 64 megabit-DRAM (Dynamic Random-Access Memory), the concentration of ultrapure total organic carbon (TOC) is a factor that determines the defective rate of semiconductor devices. This must be strictly controlled. The TOC concentration remaining in ultrapure water is known to be caused by organic nitrogen compounds derived from raw water.

In general, the method for producing ultrapure water consists of a pretreatment step, a primary pure water production step, and a secondary pure water production step. At this time, the distinction of each step is slightly different for each manufacturer, but the pretreatment step is a step for removing the sludge contained in the water to be treated by physicochemical methods such as coagulation addition method, coagulation filtration method and coagulation pressure flotation method. Here, the water to be treated means a general wide constant, hereinafter referred to as 'raw water'.

In addition, the primary pure water production step includes an ion exchange resin, degassing, and infrared sterilization, and removes ionic materials, fine particles, organic matter, dissolved gases, and live bacteria.

The second pure water production step includes ultraviolet oxidation, ion exchange resin, ultrafiltration membrane, and the like, and is a step of obtaining ultrapure water.

In such an ultrapure water production method, a treatment step using activated carbon is included as part of improving the removal efficiency of organic nitrogen compounds and carbon compounds in the primary pure water production step.

Activated charcoal treatment equipment is a device for removing organic substances in water, and is widely used from general water purification to ultrapure water production. Activated carbon also serves as a carrier for immobilizing aerobic or anaerobic microorganisms in biological treatment of water.

Activated carbon is porous and has a high internal surface area of pores and is a solid having high adsorption characteristics. Factors that determine the adsorption performance of activated carbon are known as specific surface area, pore volume, pore distribution, and the like. Adsorption characteristics of activated carbon are determined by adsorbent properties such as internal surface area, pore structure and surface chemistry of activated carbon and adsorbents such as chemical properties, molecular size, hydrophilicity and polarity of molecules. It is also determined by physicochemical conditions such as solute concentration in liquid phase, temperature, pH, and composition of the solution.

Commonly used activated carbon has an alkaline pH of about 9, and is washed with water to remove impurities or gases in activated carbon before use.

Activated carbon and ion exchange resins having such characteristics are treated first, and pretreated water is first treated, followed by second treatment with pure water using reverse osmosis membrane, etc. to obtain ultrapure water, and the obtained ultrapure water is used in a semiconductor manufacturing process. . The semiconductor manufacturing process contains a large amount of acidic materials such as hydrofluoric acid, and isopropyl alcohol or acetone is used as the organic solvent, so the pH of the organic wastewater after the semiconductor manufacturing process is acidic. About 70% of the obtained organic wastewater is used for ultrapure water production together with raw water (a wide area constant) as recovery water, and the remaining 30% is discarded as wastewater.

This series of procedures is shown in FIG.

In order to be used as recovered water, the TOC is required to be 600 ppb or less.

The pH of the recovered water is acidic, specifically about 3 to 4, as described above. Therefore, about 70% of the recovered water and raw water (wide area constant) are applied to the production of ultrapure water, so the overall atmosphere is acidic.

By the way, when the replacement capacity of activated carbon is replaced, it was confirmed that the TOC of the activated carbon treated water or the final organic wastewater increased by more than 1 ppb compared to before the replacement.

This abnormal increase in TOC subsequently raises the unsuitable ratio as the return water, thus causing a problem that can only increase the utilization rate of the raw water. Raw water has a neutral pH of about 7, so increasing the amount of its use continuously increases the pH compared to the previous one, which leads to a continuous increase of TOC. Increasing TOC plays an important role in increasing the defect rate in the semiconductor manufacturing process.

Therefore, the present inventors confirm that the above problems are not generated in the continuous ultrapure water production process but occur from the time of replacing activated carbon, which is determined to be caused by the high pH of the replacement activated carbon. As a result of using acid treated activated carbon or general alkaline activated carbon, rinsed by continuously supplying recovered water and raw water and rinsing it, it is possible to suppress the change of acidity due to the replacement of activated carbon, thereby suppressing the increase of TOC of recovered water or TOC It was found that can be lowered to complete the present invention.

Accordingly, it is an object of the present invention to provide an ultrapure water production method capable of suppressing an increase in TOC due to the increase in acidity of treated water due to the use of acid-treated activated carbon.

Ultra-pure water production method of the present invention for achieving the above object is a method for producing ultra-pure water after the pre-treatment of the raw water, after the first pure water production step including activated carbon treatment and ion exchange resin treatment, and then through a second pure water production step In the primary pure water production step, the activated carbon treatment is characterized in that it is performed using acid treated activated carbon.

Figure 1 schematically shows a general ultrapure water manufacturing process,

2 is a graph showing a change in pH as the activated carbon is washed with acidic water,

3 is a schematic diagram of a device for measuring the amount of change in TOC according to activated carbon treatment,

4 is a graph showing the result of measuring the change in TOC according to activated carbon treatment,

5 is a schematic diagram of a device for measuring the amount of change in TOC according to activated carbon treatment and ion exchange resin treatment,

6 is a graph showing the result of measuring the change in TOC according to the activated carbon treatment and the ion exchange resin treatment.

The present invention will be described in more detail as follows.

The production process of ultrapure water according to the present invention follows the known method shown in FIG. However, acid treated as activated carbon is used.

The acid treatment of the activated carbon is not particularly limited, and for example, the activated carbon is immersed in a solution such as hydrochloric acid or sulfuric acid. The pH of the activated carbon obtained after the acid treatment is preferably 3-7.

If the pH of the acid treated activated carbon is 7 or more, the TOC of the activated carbon treated water or organic wastewater after the semiconductor manufacturing process is increased as in the case of using alkaline activated carbon having a pH of 9 or higher.

After the activated carbon treatment, it is usually subjected to a degassing step and an ion exchange resin. If the pH of the activated carbon is increased, the removal efficiency of carbonic acid decreases and anionic carbonate is present in the degassing step. In the removal of ions using the anion-based ion exchange resin, the excess carbonic anion could not be removed, leading to an increase in TOC.

Meanwhile, in the present invention, it is also possible to use general alkaline activated carbon as a second alternative to using acid treated activated carbon. Generally, commercialized activated carbon of KS industrial standard has a pH of 9 or more, and before using it, it is washed with water to remove impurities or gases in activated carbon. However, even after washing with water, general activated carbon is alkaline, which increases the TOC of activated carbon treated water or organic wastewater. Thus, in the present invention, the activated carbon is washed within 24 hours with a mixed solution of pretreated recovered water and raw water used for ultrapure water production. The pH of the recovered water used and recycled in the semiconductor manufacturing process is 3 to 4 and the pH of the raw water is about 7 so that the activated carbon becomes acidic if continuously washed. Therefore, it is possible to exhibit the TOC removal efficiency equal to or higher than that of using acid treated activated carbon.

When washing with a mixture of recovered water and raw water, the pH may be adjusted according to the mixing ratio of raw water.

On the other hand, activated carbon that can be used for activated carbon treatment in the present invention is not particularly limited, but activated carbon of palm or coal type is preferable.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

Example 1 : pH change by washing general activated carbon with acidic water

The device filled with activated carbon (palm-based) for ultrapure water was continuously washed with a mixture of 70 vol% of recovered water and 30 vol% of raw water (pH 7) after being used in a semiconductor manufacturing process. The pH of activated carbon with time of washing is shown graphically in FIG. 2.

According to the results of FIG. 2, the initial pH of the commercial activated carbon is 9 or more, but the pH is gradually lowered after washing with acidic water so that the pH is about 7 after 21 hours.

Examples 2-3 and Comparative Example 1 : TOC Concentration Change after Activated Carbon Treatment

3 schematically shows an apparatus for measuring TOC concentration by using a test tube filled with activated carbon.

In this experiment, the water quality flowing into the activated carbon filled test tube was TOC 508ppb, and flowed to SV (Space Velocity) 20. Sievers-820 was used as a TOC analyzer.

Comparative Example 1 is a result of using commercially available activated carbon after immersing in water to remove impurities and gases,

Example 2 is a result of immersion in commercialized activated carbon in 100 ml of 5% hydrochloric acid and acid treatment,

Example 3 is a result of using the commercially available activated carbon after washing for 24 hours with a mixed solution of 70% by volume of recovered water and 30% by volume of raw water from which ultrapure water used in a semiconductor manufacturing process is regenerated.

In other words, Comparative Example 1 is an example for confirming the increase in TOC generated after replacing activated carbon with commercially available alkaline activated carbon as in the past, and in Example 2 to confirm the inhibition of TOC increase using acid treated activated carbon. For example, Example 3 is an example for confirming the inhibition of TOC increase by using activated carbon washed with acidic water.

The result of measuring the TOC of the treated water after passing through the test tube filled with each activated carbon through a TOC meter is shown in FIG. 4.

From the results of FIG. 4, in the case of Comparative Example 1, the TOC concentration of the first activated carbon treated water was about 200, whereas in Examples 2 and 3, the TOC was lowered by about 160 to 135 ppb, respectively. And as time passes, it turns out that the TOC density | concentration of the activated carbon treated water is much lower compared with the case of the comparative example 1 in Examples 2-3.

Thus, it can be seen that the use of acid treated activated carbon or general activated carbon after rinsing with acidic water is higher than that when the activated carbon is replaced with a commercially available pH 9 or higher.

Example 4 and Comparative Examples 2-3 : Changes in TOC Concentrations after Activated Carbon Treatment and Ion Exchange Resin Treatment

This experiment is to confirm the change of TOC concentration after using not only activated carbon treatment but also ion exchange resin treatment which is usually used in the first pure water treatment step.

Example 4 is an example of measuring the TOC concentration of the treated water, which was filled with acid treated activated carbon as in Example 3, and filled with weak anionic / strong anionic ion exchange resin as an ion exchange resin.

Comparative Example 2 was performed by washing ordinary activated carbon only with water as in Comparative Example 1 and then filling activated carbon, and using a strong cationic resin and a weak anionic / strong anionic ion exchange resin together as an ion exchange resin. It is an example that measured the TOC concentration of the treated water,

Comparative Example 3 is an example in which the TOC concentration of the treated water filled with activated carbon as in Comparative Example 2 and performed using a mixed bed ion exchange resin as the ion exchange resin.

The treatment apparatus used in this experiment was as shown in FIG. 5, and the quality of water introduced into the activated carbon filled test tube was TOC 700ppb, SV (Space Velocity) 30 was introduced, and Sievers-820 was used as a TOC analyzer. .

The result of having measured the TOC of the treated water processed by Comparative Examples 2-3 and Example 4 is shown in FIG.

From the results of FIG. 6, it can be seen that when the activated carbon treated with acid according to the present invention is used, despite the acidity of the treated water, the TOC concentration of the treated water after the ion exchange resin is low. This fact can be confirmed that the use of acid treated activated carbon does not significantly affect the subsequent processing of the ion exchange resin, etc., in order to more clearly confirm that the acid in the test tube filled with only ion exchange resin The flow rate of water (pH3.3) was 737 ppb in the influent, but the TOC concentration in the treated water was 243 ppb (67% removal). On the other hand, when the pH of the influent was 11.0, the TOC removal rate was lowered to about 64.3%.

As a result, it can be seen that the use of acid treated activated carbon has a role of increasing the TOC removal efficiency through subsequent ion exchange resin treatment.

On the other hand, even if the ion exchange resin is different from Figure 6, it can be seen that the alkaline TOC removal efficiency is lowered when alkaline activated carbon is applied (Comparative Examples 2 and 3). By the way, when the double-phase ion exchange resin is applied, the efficiency is improved compared to the case where it is not.

As a result, in the case of using the acid-treated activated carbon as in the present invention, not only does the TOC concentration of the treated water passed through the activated carbon be lowered, but also shows excellent removal efficiency even in the subsequent treatment through the ion exchange resin. have.

As described in detail above, in the case of using activated carbon acid treated with activated carbon in the primary pure water manufacturing step including pretreatment of raw water and activated carbon treatment and ion exchange resin treatment as in the present invention, the activated carbon is generated by replacing activated carbon. By effectively suppressing the increase in TOC of the treated water and organic wastewater, it is possible to increase the use rate of the recovered water and ultimately lower the defective rate of semiconductor products.

Claims (4)

In the method of producing ultrapure water after the pre-treatment of the raw water and the first pure water production step including the activated carbon treatment and ion exchange resin treatment, and then the second pure water production step, Activated carbon treatment in the first pure water production step is a method of producing ultrapure water, characterized in that is carried out using acid treated activated carbon. The method of claim 1, wherein the acid-treated activated carbon has a pH of 3 to 7. The method of producing ultrapure water according to claim 1, wherein general activated carbon rinsed with acidic water is used instead of acid treated activated carbon. 4. The method for producing ultrapure water according to claim 3, wherein the general activated carbon rinsed with acidic water is obtained by washing the general activated carbon within 24 hours with a mixed solution of recovered water and raw water having a pH of 3 to 4 before use.