JPH1085746A - Electrolytic ionic water preparation process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare highly purified ionic water for a long period of time by discharging acidic water and alkaline water for the given time and then applying reverse voltage of the pulse shape less than electrolytic voltage to a positive electrode and a negative electrode to remove metallic ions contained in the electrolytic ionic water. SOLUTION: For instance, when metallic ions are started to increase after electrolysis using the electrolytic voltage of approximately 20V is carried out for the given time, the polarity of a power source 4 is reversed, and the pulse reverse voltage of approximately -10V is applied. The pulse frequency at that time is set as approximately 0.25 Ha , and the reverse voltage application time is set as approximately one minute. During the time of power application, an acidic water discharge valve 15 and an alkaline water discharge valve 16 are closed, while an anode chamber drain outlet valve 17 and a cathode chamber drain outlet valve 18 are opened. Ionic water of increased metallic ion concentration is discharged by the arrangement. After the above treatment, the polarity of the power source 4 is reversed, and the voltage is reversed by approximately 20V, and the opening and closing of valves 15-18 are also reversed. The supply of ionic water is restarted by the arrangement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing electrolytic ionic water, and more particularly to a method for producing high-purity electrolytic ionic water used for cleaning semiconductor substrates.

[0002]

2. Description of the Related Art Conventionally, cleaning of a semiconductor wafer has been generally carried out using an aqueous solution of a high-purity acid or alkali. However, as the diameter of semiconductor wafers increases, the amount of acid and alkali used increases, and the cost of the cleaning process, including the cost of wastewater treatment, continues to increase.

Therefore, the present inventor electrolyzes, for example, tap water used in the medical field to produce alkaline ionized water used as medical drinking water and acidic ionized water used for disinfection. Using an electrolytic ionized water generator, an attempt was made to electrolyze high-purity pure water instead of the conventional acid and alkali aqueous solutions and use the electrolytic ionized water of acidic water and alkaline water for cleaning semiconductor wafers.

Next, the above-mentioned attempt will be described. FIG.
(A) shows an outline of a main part of an electrolytic ionized water generator,
FIG. 2B shows a generator unit.

As shown in FIG. 2A, the electrolytic ionic water generator comprises five generator units 100. Each unit 100 is formed by an ion exchange membrane 2 as shown in FIG. 2B. It has an electrolytic cell 1 divided into an anode chamber 1a and a cathode chamber 1b. A positive electrode 3a made of platinum is inserted in the anode chamber 1a, and a negative electrode 3b made of titanium is inserted in the negative electrode 1b, so that an electrolytic current flows from an electrolytic power supply 4. The electrolytic cell 1 is provided with a raw water supply port 5a communicating with the anode chamber 1a and a raw water supply port 5b communicating with the cathode chamber 1b. On the other side, a water discharge port 6a for discharging acidic water and a drain port 7a for the anode chamber are provided. , An outlet 6b for discharging alkaline water, and a drain 7 for the cathode chamber
b are provided respectively. Then, as shown in FIG. 2A, the raw water supply ports 5a and 5b of each unit 100 are the raw water supply pipe 8, the acidic water discharge port 6a is a common discharge pipe 9, and the alkaline water discharge port 6b is a common discharge port. The water pipe 10 and the drain port 7a of the anode chamber are connected to a common drain pipe 11, and the drain port 7b of the cathode chamber is connected to a common drain pipe 12. In addition, 1
3, 14, 15, 16, 17, and 18 are all valves.

Next, a method for producing electrolytic ionic water using the electrolytic ionic water producing apparatus will be described. First, high-purity pure water is supplied to the raw water supply pipe 8 as raw water, pure water is supplied from the raw water supply port 5a into the anode chamber 1a, and from the raw water supply port 5b into the cathode chamber 1b, and then the positive electrode 3a and the negative electrode are supplied. 3b, electricity is generated, and pure water is electrolyzed to electrolyze acidic water in the anode chamber 1a and alkaline water in the cathode chamber 1b. Then, the acidic water generated in each unit 100 is taken out from a common water discharge pipe 9 from the water discharge port 6a, and the alkaline water is taken out to a common alkaline water discharge pipe 10 from the water discharge port 6b.

[0007]

However, when electrolytic ionic water is continuously generated for a long time using such an electrolytic ionic water generator, platinum, which is a constituent material of the electrode, is converted from the positive electrode and the negative electrode. Metal ions such as iron and chromium dissolve in ionic water.

Since these metal ions are positive ions, they are attracted to the negative electrode 3b by the applied electric field,
It does not adhere to the negative electrode 3b and gathers near the electrode. Then, these metal ions are mixed into the alkaline ionized water, and are extracted from the alkaline water discharge port 6b through a common alkaline water discharge pipe 10.

In a semiconductor device, since the electrical characteristics are greatly affected by the adhesion of a small amount of metal ions, it is necessary to remove metal ions contained in electrolytic ionized water.

In order to remove the high concentration of metal cations around the negative electrode, a reverse voltage may be applied between the positive electrode and the negative electrode. Thereby, metal cations around the negative electrode are easily removed. However, in this case, the following inconvenience occurs. That is, when a reverse voltage equal to or higher than the electrolytic voltage is applied, the original positive electrode acts as a negative electrode, and metal ions gather around the original positive electrode. In addition, the original negative electrode acts as a positive electrode, and newly elutes metal ions. As a result, the metal ion concentration in the electrolytic ionic water is rather increased. The present invention has been made in view of the above problems, and has as its object to produce and supply high-purity electrolytic ionized water from which metal ions have been removed for a long time.

[0011]

In order to solve the above problems, in the method for producing electrolytic ionic water according to the present invention, a raw water supply port is provided in an anode chamber and a cathode chamber formed by dividing an electrolytic cell by a diaphragm. Through which raw water is filled, an electrolytic voltage is applied between the positive electrode inserted into the anode chamber and the negative electrode inserted into the cathode chamber, and the raw water filled into the anode chamber is converted into acidic water, and The raw water filled in the cathode compartment is electrolytically separated into alkaline water, respectively, and the acidic water is taken out from an acid water take-out port connected to the anode compartment, and the alkaline water is taken out from an alkaline water take-out port connected to the cathode compartment. In the method for producing electrolytic ionic water taken out from the above, after taking out the acidic water and the alkaline water for a certain time, a reverse voltage equal to or lower than the electrolytic voltage is applied between the positive electrode and the negative electrode. It is applied to the scan form and removing the metal ions contained in the electrolytic ion water.

[0012] Further, in accordance with the application time of the reverse voltage, the outlet of the alkaline water is switched from the outlet of the alkaline water to the outlet.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in detail with reference to the drawings. In the embodiment of the present invention, the electrolytic ionized water generator shown in FIG. 2 is used. FIG.
(A) shows an outline of a main part of an electrolytic ionized water generator,
FIG. 2B shows a generator unit.

As shown in FIG. 2A, the electrolyzed ionic water generator comprises five generator units 100. Each unit 100 has an ion exchange membrane 2 as shown in FIG. 2B. It has an electrolytic cell 1 divided into an anode chamber 1a and a cathode chamber 1b. A positive electrode 3a made of platinum is inserted in the anode chamber 1a, and a negative electrode 3b made of titanium is inserted in the negative electrode 1b, so that an electrolytic current flows from an electrolytic power supply 4. The electrolytic cell 1 is provided with a raw water supply port 5a communicating with the anode chamber 1a and a raw water supply port 5b communicating with the cathode chamber 1b. On the other side, a water discharge port 6a for discharging acidic water and a drain port 7a for the anode chamber are provided. , An outlet 6b for discharging alkaline water, and a drain 7 for the cathode chamber
b are provided respectively. Then, as shown in FIG. 2A, the raw water supply ports 5a and 5b of each unit 100 are the raw water supply pipe 8, the acidic water discharge port 6a is a common discharge pipe 9, and the alkaline water discharge port 6b is a common discharge port. The water pipe 10 and the drain port 7a of the anode chamber are connected to a common drain pipe 11, and the drain port 7b of the cathode chamber is connected to a common drain pipe 12. In addition, 1
3, 14, 15, 16, 17, and 18 are all valves.

Next, a method for producing electrolytic ionic water using the electrolytic ionic water producing apparatus will be described. First, high-purity pure water is supplied to the raw water supply pipe 8 as raw water, pure water is supplied from the raw water supply port 5a into the anode chamber 1a, and from the raw water supply port 5b into the cathode chamber 1b, and then the positive electrode 3a and the negative electrode are supplied. 3b, electricity is generated, and pure water is electrolyzed to electrolyze acidic water in the anode chamber 1a and alkaline water in the cathode chamber 1b. Then, the acidic water generated in each unit 100 is taken out from a common water discharge pipe 9 from the water discharge port 6a, and the alkaline water is taken out to a common alkaline water discharge pipe 10 from the water discharge port 6b.

When the electrolytic ionic water is continuously generated for a long time, platinum, which is an electrode material, is removed from the anode chamber and the cathode chamber.
Metal ions such as iron and chromium dissolve in the ionic water and contaminate the ionic water. Therefore, it is necessary to release and remove metal ions around the electrodes.

Hereinafter, a method of removing metal ions will be described with reference to FIG. FIG. 1 shows a relationship between an electrolysis voltage and a valve operation during generation of electrolyzed water according to the embodiment of the present invention.

In FIG. 1, the elapsed time is shown on the horizontal axis.
The vertical axis represents the positive electrode 3a in the generator shown in FIG.
An applied voltage is applied between the negative electrodes 3b. Also,
The valve 15 shown in FIG.
The open / closed state of 16, 17, 18 is shown.

The contents of FIG. 1 will be described below in time. After performing electrolysis at an electrolysis voltage of 20 V for a certain period of time, at the time when the number of metal ions starts to increase, the polarity of the power supply 4 in FIG. here,
The pulse frequency may be 0.25 (Hz) and the reverse voltage application time may be one minute. During the application of the pulse voltage, the acidic water discharge valve 15 and the alkaline water discharge valve 16 which are open when the electrolytic water is generated are closed, and the anode chamber drain valve 17 and the cathode chamber discharge valve 18 which are closed when the electrolytic water is generated.
open. As a result, ion water having an increased metal ion concentration during application of the pulse voltage is discharged. After this operation is continued for about 1 minute, the polarity of the power supply 4 shown in FIG.
Increase the applied voltage to 20V, and at the same time
5. The alkaline water discharge valve 16 is opened, and the anode chamber drain valve 17 and the cathode chamber drain valve 18 are closed. Thereby, ion water can be supplied again.

As described above, since metal cations are mainly collected around the negative electrode, when there is little contamination by ions around the positive electrode, only alkaline water is discharged during pulse voltage application, and acidic water is discharged. Can be used as usual.

FIG. 3 shows how the relative concentration (residual rate) of iron ions remaining in the anode chamber 1a and the cathode chamber 1b during the application of the pulse voltage changes. As shown here, immediately after the application of the pulse voltage, the residual iron ions rapidly decrease, and high-concentration iron ion wastewater is discharged into the wastewater. Thereafter, the residual iron ion concentration gradually decreases and stabilizes in about 40 seconds.
Actually, the iron ion concentration in the waste water, which was about 500 (ppt) before the pulse voltage was applied, was reduced to 10 (ppt) or less after the pulse voltage was applied for 1 minute.

Thereafter, by repeating this operation, high-purity ion water can be supplied stably for a long period of time. In the above-described embodiment, the state of the concentration change has been described by taking iron ions as an example. However, the application of the present invention is not limited to this, and the same applies to all metal impurities such as platinum and chromium. Can be.

Further, in the above embodiment, 10 V,
Although an example in which a pulse reverse voltage of 0.25 (Hz) is applied for one minute has been described, the pulse voltage, pulse interval, and pulse application time are not limited to these, but may be determined according to the shape of the ion water generator and the generation conditions. Just set it. In the above embodiment, the electrolysis voltage is set to 20 V, but it is needless to say that the present invention is not limited to this.

[0024]

According to the present invention, electrolytic ion water having a low metal ion concentration can be produced stably.

[Brief description of the drawings]

FIG. 1 shows correspondence between an electrolytic voltage and a valve opening / closing in a method for producing electrolytic ionic water according to an embodiment of the present invention.

FIG. 2 shows an electrolytic ionic water generator used for electrolytic ionic water generation according to an embodiment of the present invention.

FIG. 3 shows the inside of the anode chamber 1a and the cathode chamber 1b during application of a pulse voltage.
3 shows how the relative concentration (residual rate) of iron ions remaining in the inside changes.

[Explanation of symbols]

 1 ... Electrolyzer 1a ... Anode chamber 1b ... Cathode chamber 2 ... Diaphragm 3a ... Positive electrode 3b ... Negative electrode 4 ... Electrolysis power supply 5a, 5b ... Raw water supply port 6a ・ ・ ・ Acid water discharge port 6b ・ ・ ・ Alkaline water discharge port 7a ・ ・ ・ Anode chamber drain port 7b ・ ・ ・ Cathode chamber drain port 8 ・ ・ ・ ・ Raw water supply pipe 9 ・ ・ ・ ・ Acid water Common discharge pipe 10 ・ ・ ・ Alkaline water common discharge pipe 11 ・ ・ ・ Anode chamber drain common drain pipe 12 ・ ・ ・ Cathode chamber drain common drain pipe 15 ・ ・ ・ Acid water discharge valve 16 ・ ・ ・ Alkaline water discharge valve 17 ・ ・ ・ Anode water drain valve 18 ・ ・ ・ Cathode water drain valve 100 ・ ・ Generation unit

Claims (2)

[Claims] 1. An anode chamber and a cathode chamber formed by dividing an electrolytic cell by a diaphragm are each filled with raw water through a raw water supply port, and are inserted into the anode chamber and the cathode chamber. An electrolytic voltage is applied between the negative electrode and the raw water filled in the anode chamber into acidic water, and the raw water filled in the cathode chamber is electrolytically separated into alkaline water. Taking out from the acidic water outlet connected to the chamber, the alkaline water is taken out from the alkaline water outlet connected to the cathode chamber, in the electrolytic ionic water generation method, the acidic water for a certain time,
After taking out the alkaline water, a reverse voltage less than the electrolytic voltage is applied in a pulsed manner between the positive electrode and the negative electrode to remove metal ions contained in the electrolytic ionic water. Method. 2. The method according to claim 1, wherein the outlet of the alkaline water is switched from the outlet of the alkaline water to the outlet in conjunction with the application time of the reverse voltage. .