JP5376152B2 - Sulfuric acid electrolysis method - Google Patents

Description

  The present invention relates to a method for producing a functional chemical solution containing persulfuric acid (peroxomonosulfuric acid, peroxodisulfuric acid) ions by electrolyzing sulfuric acid, and in particular, an unnecessary ion implanted into an electronic material such as a silicon wafer. The present invention relates to a method capable of supplying the functional chemical liquid as a cleaning liquid used in a cleaning method for peeling and cleaning organic contaminants such as a resist.

  In a conventional resist stripping process for removing an unnecessary resist ion-implanted into an electronic material such as a silicon wafer, a solution called SPM in which concentrated sulfuric acid and hydrogen peroxide solution are mixed is used. Since the method using this solution consumes a large amount of sulfuric acid and hydrogen peroxide solution, the running cost is high, and a large amount of waste liquid is generated. In contrast, the present inventors have already used an electrolytic sulfuric acid solution containing an oxidizing substance such as peroxodisulfuric acid or peroxomonosulfuric acid (hereinafter collectively referred to as persulfuric acid) obtained by electrolyzing sulfuric acid as a cleaning solution. And a cleaning method and a cleaning system that circulate and use sulfuric acid have been developed (for example, Patent Documents 1 and 2). With these cleaning methods and systems, it is possible to reduce the amount of chemical solution used and the amount of waste liquid and at the same time obtain a high cleaning effect.

  Further, the present inventors further have a processing method and a method in which in a wafer cleaning system using an electrolytic sulfuric acid solution as a cleaning liquid, a diaphragm is incorporated between the anode and the cathode, and the electrolysis is performed by dividing the anode chamber and the cathode chamber. Developed a device (Patent Document 3), uses a fluororesin cation exchange membrane (for example, “Nafion”) as the diaphragm, and uses sulfuric acid with a sulfuric acid concentration of 0.1-18M as the electrolyte used for the catholyte It is preferable to do this.

  On the other hand, Non-Patent Document 1 describes that the fluororesin-based cation exchange membrane is dehydrated due to the anolyte 96% by mass sulfuric acid and the catholyte 70% by mass sulfuric acid, resulting in insufficient conductivity and damage. In addition, an electrolysis apparatus for performing diaphragm electrolysis processing, which is limited to a sulfuric acid concentration of 96% by mass or more in the anolyte has been proposed (Patent Document 4). In this patent document, when electrolysis is performed by supplying 96% by mass or more of high-concentration sulfuric acid to the anode chamber, it is preferable to supply 70% by mass or less of sulfuric acid in order to supply water from the cathode chamber to the ion exchange membrane. It has been shown.

JP 2006-114880 A JP 2006-278687A JP 2006-228899 A JP 2007-332441 A

“Examination of concentrated sulfuric acid electrolysis using conductive diamond electrode”, Proceedings of Joint Lecture on Applied Physics, Vol54thNo. 2, Page 829

  However, when conducting electrolytic membrane treatment, if the electrolytic current density is set high using high-concentration sulfuric acid for efficient use of the apparatus, the fluororesin cation exchange membrane used as the diaphragm is damaged in a short time. It was newly found that this problem occurs. On the other hand, when the electrolysis current density is set low in order to suppress the damage to the diaphragm, there is a problem that the production efficiency of persulfuric acid is lowered and the efficiency of the apparatus is lowered.

  The present invention has been made against the background of the above circumstances, and even when concentrated sulfuric acid is electrolyzed at a high current density by a diaphragm-type electrolysis apparatus, it is possible to perform good energization without damaging the diaphragm for a long period of time. An object of the present invention is to provide an electrolysis method that can be used.

That is, of the present invention, the sulfuric acid electrolysis method of the first present invention is a sulfuric acid electrolysis method in which electrolysis is performed using sulfuric acid as a catholyte and an anolyte of a diaphragm type electrolysis cell having an anode and a cathode constituted by diamond electrodes . , When the sulfuric acid concentration of the anolyte is less than 80 to 96% by mass , the liquid flow rate in the anode chamber and the cathode chamber is 10 m / h or more , and the electrolytic current density is 0.1 to 1.0 A / cm ² ; The sulfuric acid concentration of the catholyte is 10 to 50% by mass, the liquid temperatures of the anolyte and the catholyte are 40 to 70 ° C., and used for 10 hours or more .

  The sulfuric acid electrolysis method of the second aspect of the present invention is characterized in that, in the first aspect of the present invention, the diaphragm provided with the diaphragm type electrolytic cell is a fluororesin cation exchange membrane.

  According to the present invention, by appropriately setting the sulfuric acid concentration of the catholyte and the temperature of the anolyte and catholyte, efficient electrolysis can be performed while suppressing damage to the diaphragm. Below, the conditions prescribed | regulated by this invention are demonstrated.

Anolyte sulfuric acid concentration: less than 80 to 96% by mass The anolyte has a low detergency when the sulfuric acid concentration is too low. For this reason, the lower limit of the sulfuric acid concentration of an anolyte shall be 80 mass%.

Electrolytic current density 0.1-1.0 A / cm ²
It is widely known that peroxodisulfate ions are generated by electrolyzing sulfate ions, and oxidation reactions of reaction formulas 1 and 2 occur in the anode chamber.
2SO ₄ ²⁻ → S ₂ O ₈ ²⁻ + 2e ⁻ .
2HSO ₄ ²⁻ → S ₂ O ₈ ²⁻ + 2H ⁺ + 2e ⁻ Formula 2
Thus, in order to generate peroxodisulfate ions, it is necessary to dissociate into monovalent or divalent sulfate ions. In addition, since the amount of peroxodisulfate ions generated is greatly affected by the amount of current supplied, in order to reduce the manufacturing cost of the apparatus, the input current is increased as much as possible for a certain electrode area, that is, the current density is increased. It is preferable to do. However, in the case of sulfuric acid having a high concentration such as a sulfuric acid concentration of 80 to less than 96% by mass, the proportion of molecular sulfuric acid is high, and when electrolysis is performed at an excessively high current density, the supply of sulfate ions to the vicinity of the anode surface becomes rate-limiting, The amount of peroxodisulfate ions produced does not increase. Further, when the supply of sulfate ions is insufficient, there is a possibility of causing electrode wear. Thus, the electrolytic current density is preferably in the range of 0.1~1.0A / dm ^2.

Catholyte sulfuric acid concentration: 10-50% by mass
In order for a diaphragm such as a fluororesin cation exchange membrane to have high cation conductivity, it is necessary to contain water in the resin constituting the diaphragm. If the water in the resin is insufficient, the mobility of H ⁺ decreases, and if it is extremely insufficient, the resistance of the diaphragm also increases, resulting in physical destruction of the diaphragm. When the sulfuric acid concentration of the anolyte in the present invention is less than 80 to 96% by mass, the diaphragm is damaged if the linear velocity in the anode chamber is 10 m / h or more even at a high current density of 0.1 to 1.0 A / cm ^2. Although a small amount of H ⁺ ions can be supplied, it is not possible to ensure sufficient supply of water to maintain conductivity from the anode side to the diaphragm. Therefore, it is necessary to reduce the sulfuric acid concentration on the cathode side and supply water from the cathode side to the diaphragm by osmotic pressure. On the other hand, if the sulfuric acid concentration in the catholyte is lowered too much, the conductivity is lowered and the energy efficiency is lowered due to the increase in interelectrode voltage, or the osmotic pressure from the catholyte side to the anolyte side is Lower than the desired concentration. Therefore, the sulfuric acid concentration of the cathode needs to be in the range of 10 to 50% by mass.

Liquid temperature of catholyte and anolyte: 40 to 70 ° C
Since the fluororesin-based cation exchange membrane used for the diaphragm is thermoplastic, when the liquid temperature becomes high, the mechanical strength is lowered and may be damaged by the pressure difference between the anode chamber and the cathode chamber. For example, when the liquid temperature of the catholyte exceeds 70 ° C., the supply of water to the diaphragm is insufficient due to an increase in the water vapor pressure, so that sufficient electrical conductivity cannot be ensured and breakage occurs. On the other hand, if the liquid temperature is too high, the electrolysis efficiency is extremely lowered. Therefore, the rising value of the liquid temperature is 70 ° C., preferably 60 ° C. Conversely, as the liquid temperature becomes lower, the ion flux decreases due to the increase in the viscosity of the liquid, which is not preferable because the conductivity of the liquid decreases and the electrode voltage increases and the wear rate of the electrode increases. Furthermore, it is necessary to warm to a high temperature when supplying to the cleaning side, but if the temperature of the electrolyte is too low, the heat energy for heating becomes enormous. Therefore, the lower limit of the catholyte and anolyte liquid temperatures is 40 ° C.

Diaphragm: Fluororesin cation exchange membrane As the trade name “Nafion” (manufactured by DuPont) made of perfluorosulfonic acid, fluorinated resin cation exchange membranes are resistant to oxidation and have high conductivity. It is generally used as a diaphragm for an electrolyzer according to the purpose. When electrolysis is performed using this as a diaphragm, the various cations present in the anolyte move to the cathode chamber and show conductivity. In the present invention, the anolyte is 80 to 96 [wt. %] Sulfuric acid is allowed to flow, so that the H ⁺ ions in the anode chamber move to the cathode chamber and the electrolytic reaction proceeds.
Although the increase in voltage can be suppressed by reducing the thickness of the diaphragm, the mechanical strength is insufficient, and there is a risk of damage due to the pressure difference between the anode chamber and the cathode chamber. In addition, pinholes are likely to occur, and by-product gases such as oxygen or hydrogen generated by electrolysis cross over between the membranes, and it is very dangerous to produce explosive gases, so a certain film thickness is required. It is preferable that it is 0.01 mm or more. However, if the film thickness is too large, resistance increases and electrolysis efficiency decreases, so the upper limit of the film thickness is preferably 0.5 mm or less.
The above is the same regardless of whether the structure of the electrolytic cell is a counter electrode type or a bipolar type.

Electrode Configuration The electrode provided in the electrolysis cell for performing the electrolysis method of the present invention is not particularly limited in material as the present invention, but the diamond electrode can efficiently generate persulfate ions, This has the advantage of low wear. Therefore, among the electrodes of the electrolytic reaction apparatus, it is desirable that at least the anode on which sulfate ions are generated is composed of a diamond electrode, and both the anode and the cathode can be composed of diamond electrodes. Also in the bipolar electrode, it is desirable to coat the side to be the anode with diamond, and it is more preferable to coat the opposite surface with diamond.
A conductive diamond electrode is formed by using a semiconductor material such as a silicon wafer or a metal material as a substrate, synthesizing a conductive diamond thin film on the surface of the substrate, and then removing the substrate by melting or the like. Self-standing type conductive polycrystalline diamond deposited and synthesized in a shape can be mentioned. A substrate-covered type laminated on a metal substrate such as Si, Nb, W, or Ti can also be used. In order to obtain the mechanical strength with the self-stand type, it is necessary to increase the thickness of the diamond layer to be formed, which is uneconomical.
As the conductive diamond electrode, a plate-like one is usually used, but a plate having a network structure can also be used, and the electrode shape is not particularly limited in the present invention. The electrode can be either a counter electrode type or a bipolar type.

The present invention relates to a diaphragm-type electrolysis apparatus having a fluororesin-based cation exchange membrane or the like as a diaphragm, using an anode and a cathode composed of diamond electrodes, and an electrolysis current density of 0.1 to 1.0 A / dm ² , and When electrolysis is carried out at a sulfuric acid concentration of the anolyte of 80 to less than 96% by mass and a liquid passage speed of 10 m / h or more in the anode chamber and the cathode chamber, the sulfuric acid concentration of the catholyte is 10 to 50% by mass. Further, by setting the temperature of the catholyte to 40 to 70 ° C., sufficient conductivity can be secured, and there is an effect that the diaphragm can be prevented from being damaged or performance deteriorated even when used for a long time.

It is the schematic which shows the washing | cleaning system with which the electrolysis method of one Embodiment of this invention is implemented. Similarly, it is a figure which shows the detail of the diaphragm type electrolysis cell contained in this washing | cleaning system.

  Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a schematic view showing a cleaning system for carrying out the electrolysis method of the present invention.

The cleaning system mainly includes a single wafer cleaning machine 1, a diaphragm electrolytic cell 20, and a circulation line including a feed pipe and a return pipe, which will be described later.
The single wafer cleaning machine 1 is provided with a nozzle 2, and the tip side ejection portion of the nozzle 2 is located in the single wafer cleaning machine body. In the single wafer cleaning machine 1, a substrate mounting table 3 is installed in the jetting direction of the nozzle 2 so that the semiconductor substrate 100 that is a material to be cleaned can be mounted and rotated.

  On the other hand, as shown in detail in FIG. 2, the diaphragm type electrolytic cell 20 includes an anode 21, a cathode 22, and a bipolar electrode 23, and a current supply device (not shown) is connected to the anode 21 and the cathode 22. Further, a diaphragm 24 made of a fluororesin cation exchange membrane is disposed between the anode 21 and the electrode surface serving as the cathode of the bipolar electrode 23, and between the electrode surface serving as the anode of the bipolar 23 and the cathode 22. Similarly, a diaphragm 25 made of a fluororesin cation exchange membrane is disposed, and the electrodes 24 are partitioned into anode chambers 26a and 27a and cathode chambers 26b and 27b by the diaphragms 24 and 25, respectively. Note that the present invention is not limited to the bipolar type, and may include only an anode and a cathode as electrodes. In this embodiment, the anode 21, the cathode 22, and the bipolar electrode 23 are constituted by diamond electrodes. The diamond electrode is produced by forming a diamond thin film on a substrate and doping boron in a range of preferably 50 to 20000 ppm with respect to the carbon content of the diamond thin film.

In the single wafer cleaning machine 1, as shown in FIG. 1, a feed pipe 31 b of a circulation line for circulating a sulfuric acid solution between the nozzle 2 and the diaphragm type electrolytic cell 20 is connected to the nozzle 2. A heating device 13 is provided in the feed pipe 31b immediately before connection to the nozzle 2, and a sulfuric acid solution containing persulfate ions supplied to the nozzle 2 is preferably set at a liquid temperature of 100 to 190 ° C. at the nozzle outlet. Heat so that it becomes transient.
In addition, a return line 30a of a circulation line is connected to the drainage section of the single wafer cleaning machine 1, and a sulfuric acid drainage tank 4 is provided in the return pipe 30a for storing and temporarily storing drainage. It is installed. The return pipe 30a on the downstream side of the sulfuric acid drainage tank 4 is provided with a liquid feed pump 5 for feeding a sulfuric acid solution, a filter 6 for removing a solid residue of a resist that cannot be decomposed with the sulfuric acid solution, and a sulfuric acid solution being cooled. A cooler 7 is interposed in sequence. The downstream end of the return pipe 30 a is connected to the storage tank 8.

The storage tank 8 is connected with an ultrapure water supply line 17a for supplying ultrapure water and a concentrated sulfuric acid supply line 17b for supplying concentrated sulfuric acid solution. The ultrapure water supply line 17a and the concentrated sulfuric acid supply line 17b may be connected to appropriate places in the circulation line.
An upstream end of a feed pipe 30b is connected to the storage tank 8, and a feed pump 9 for feeding the solution toward the downstream side, and a cooling for cooling the solution are connected to the feed pipe 30b. The vessel 10 is sequentially provided, and the downstream end of the feed pipe 30b is connected to the liquid inlet side of the anode chambers 26a and 27a of the diaphragm type electrolysis cell 20. An upstream end of a feed pipe 31a is connected to the liquid discharge side of the anode chambers 26a and 27a, a gas-liquid separation tank 11 is interposed in the feed pipe 31a, and a downstream end of the feed pipe 31a is , Connected to the storage tank 8. Further, the upstream end of the feed pipe 31b is connected to the storage tank 8, and the feed pipe 12b for feeding the solution toward the downstream side and the heating device 13 are connected to the feed pipe 31b. And the downstream end of the feed pipe 31b is connected to the nozzle 2 of the single wafer cleaning machine 1 as described above.

  Further, as shown in FIG. 2, the downstream end of the feed pipe 32 is connected to the liquid inlet side of the cathode chambers 26b and 27b of the diaphragm type electrolysis cell 20, and the feed pipe 32 feeds the catholyte. The upstream end is connected to the catholyte reservoir 14 via the liquid pump 15. The upstream end of the return pipe 33 is connected to the liquid discharge side of the cathode chambers 26b and 27b. The return pipe 33 is provided with a gas-liquid separation tank 16 and has a downstream end connected to the catholyte storage tank 14. The catholyte storage tank 14 is connected to an ultrapure water supply line 18a for supplying ultrapure water and a concentrated sulfuric acid supply line 18b for supplying concentrated sulfuric acid solution.

Next, the operation of the cleaning system will be described. Concentrated sulfuric acid is accommodated in the storage tank 8 from the sulfuric acid supply line 17b, and ultrapure water is mixed in a predetermined volume ratio from the ultrapure water supply line 17a. A sulfuric acid solution with a predetermined concentration is used. Note that ultrapure water or concentrated sulfuric acid may be appropriately supplied to adjust the sulfuric acid concentration as the cleaning system is operated.
The sulfuric acid solution in the storage tank 8 is sequentially fed to the liquid inlet side of the anode chambers 26 a and 27 a of the diaphragm type electrolysis cell 20 by the liquid feed pump 9. At this time, the sulfuric acid solution is cooled to a predetermined temperature by the cooler 10. With the above settings, the sulfuric acid solutions at the inlets and outlets of the anode chambers 26a and 27a are adjusted to a sulfuric acid concentration of 80 to 96% by mass and a liquid temperature of 20 to 70 ° C. during electrolysis, which will be described later. Therefore, the liquid temperature at the inlet is 20 ° C. or higher and the liquid temperature at the outlet is 70 ° C. or lower.

  On the other hand, concentrated sulfuric acid is accommodated in the catholyte storage tank 14 from the sulfuric acid supply line 18b, and ultrapure water is mixed into the catholyte supply line 18b at a predetermined volume ratio from the ultrapure water supply line 18a. Prepare to reach temperature. Ultrapure water or concentrated sulfuric acid may be supplied as needed to adjust the sulfuric acid concentration and temperature as the cleaning system operates. The sulfuric acid solution in the catholyte storage tank 14 is sequentially fed to the liquid inlet side of the cathode chambers 26 b and 27 b of the diaphragm type electrolysis cell 20 by the liquid feed pump 15. According to the above settings, the sulfuric acid solution is adjusted to a concentration of 10 to 50% by mass and a temperature of 20 to 70 ° C. at the inlet and outlet of the cathode chambers 26b and 27b during the electrolysis described later according to the above settings. Since the liquid temperature at the outlet is higher than the liquid temperature at the inlet, the liquid temperature at the inlet is 20 ° C. or higher and the liquid temperature at the outlet is 70 ° C. or lower.

In the diaphragm type electrolytic cell 20, when the anode 21 and the cathode 22 are energized by the energizing device, the bipolar electrode 23 is polarized, and the cathode and the anode appear on the opposing surfaces of the anode 21 and the cathode 22. In the energization, the energization is controlled so that the current density on the diamond electrode surface is 0.1 to 1.0 A / cm ² .

When energized in the diaphragm type electrolysis cell 20, H ⁺ ions in the solution flowing through the circulation line are smoothly supplied from the diaphragms 24 and 25 to the cathode side in the anode chambers 26a and 27a, and good conductivity is obtained.
In the anode chambers 26a and 27a, sulfate ions are oxidized to generate persulfate ions, and oxygen gas is generated as a by-product. At this time, since the persulfate ions are prevented from moving to the cathode chambers 26b and 27b by the diaphragms 24 and 25, it can be avoided that the persulfate ions are reduced on the cathode side and returned to the sulfate ions. In the cathode chamber, hydrogen ions are reduced to generate hydrogen gas, which is discharged out of the diaphragm type electrolysis cell 20 as the liquid passes.
At this time, water in the sulfuric acid solution is supplied to the diaphragms 24 and 25 side by osmotic pressure due to a difference in concentration between the sulfuric acid solution on the anode chambers 26a and 27a side and the sulfuric acid solution on the cathode chambers 26b and 27b side. The movement of H ⁺ is made smoothly.

The sulfuric acid solution containing persulfate ions sent out from the anode chambers 26a and 27a is sent from the feed pipe 31a to the storage tank 8. At this time, oxygen gas generated by electrolysis is removed by the gas-liquid separation tank 16 . The sulfuric acid solution sent out from the cathode chambers 26 b and 27 a is sent from the feed tube 33 to the catholyte storage tank 14. At this time, hydrogen gas generated by electrolysis is removed by the gas-liquid separation tank 16.
The sulfuric acid solution stored in the storage tank 8 is fed to the single wafer cleaning machine 1 side by the liquid feed pump 12 through the feed pipe 31b. The sulfuric acid solution to be fed is heated by the heating device 13 and supplied to the nozzle 2.

In the single wafer cleaning machine 1, high-temperature sulfuric acid droplets heated to 100 to 190 ° C. are ejected from the nozzle 2 for a certain period of time. A semiconductor substrate 100 is installed on the substrate mounting table 3, the semiconductor substrate 100 is rotated by the substrate mounting table 3, the surface of the semiconductor substrate 100 is cleaned by sulfuric acid droplets containing persulfate ions, and a resist or the like is formed. Stripping and removal are performed. The ejected sulfuric acid solution is scattered and dropped after the substrate 100 is washed, and the dissolved resist and the like are discharged to the feed tube 30a. It is temporarily stored in the sulfuric acid drainage tank 4. In the sulfuric acid drain tank 4, the decomposition of the resist melt contained in the sulfuric acid solution proceeds. The sulfuric acid solution in the sulfuric acid drainage tank 4 is fed to the storage tank 8 side by the liquid feed pump 5. At this time, the solid residue contained in the sulfuric acid solution is removed by the filter 6, and then the sulfuric acid solution is cooled to 30 to 60 ° C. by the cooler 7 and introduced into the storage tank 8.

The sulfuric acid solution stored in the storage tank 8 is then sent to the diaphragm-type electrolytic cell 20 in the same manner as described above, and the sulfuric acid solution whose persulfate ion concentration is reduced by autolysis is electrolyzed to convert persulfate ions from the sulfate ions. The persulfate ions are regenerated and stored again in the storage tank 8, and then returned to the single-wafer cleaning machine 1 and used as a cleaning liquid in the same manner as described above.
In the above embodiment, the single wafer type was used as the washing machine, but a batch type washing tank may be used as the present invention.
Furthermore, the present invention is not limited to the contents of the above-described embodiments, and appropriate modifications can be made without departing from the scope of the present invention.

[Example 1]
The electrolytic apparatus shown in FIG. 2 incorporates a fluororesin cation exchange membrane (trade name “Nafion 117”, thickness 0.2 mm) as a diaphragm, and the anolyte conditions, catholyte conditions and current density are as shown in Table 1. The diaphragm evaluation test was performed for up to 10 hours by shaking. The evaluation was terminated when the anolyte and the catholyte were mixed, and the test was terminated. The diaphragm that was not damaged was taken out of the electrolyzer for 10 hours from the start of electrolysis, surface observation and IEC (ion exchange capacity) analysis. Went. The IEC before the Nafion 117 test was 0.9 to 1.1 meq / g. Moreover, the liquid temperature of the anolyte and the catholyte was shown by inlet temperature (degreeC)-outlet temperature (degreeC).
The test results are shown in Table 1.
As a result of these tests, the sulfuric acid concentration of the catholyte when electrolyzed at a sulfuric acid concentration of 80 to 96 mass%, a liquid temperature of 50 to 60 ° C., and a current density of 0.1 to 1.0 A / cm ^{2 as} in the inventive examples. If it was in the range of 10-50 mass% and liquid temperature 20-70 degreeC, it was possible to prevent the damage of a diaphragm, without the electroconductivity of a liquid falling and an electrode voltage rising.

[Example 2]
A fluororesin cation exchange membrane (trade name “Nafion117”, thickness 0.2 mm) was incorporated as a diaphragm in the electrolysis apparatus shown in FIG. 2, and electrolysis was performed under the following electrolysis conditions. After 2000 hours of operation, the incorporated diaphragm was taken out, and FT-IR analysis and ion exchange capacity (IEC) measurement of the diaphragm surface were performed. As a result, there was no change compared with the FT-IR spectrum before use, and the IEC value hardly decreased from 1.0 meq / g before use to 1.0 meq / g after use.

<Electrolysis conditions>
Anode: 85-95 mass% sulfuric acid, liquid temperature 50-70 ° C., liquid flow rate 20 m / h
Cathode: 10-50 mass% sulfuric acid, liquid temperature 40-50 ° C., liquid flow rate 20 m / h
Input current: 50A
Electrolytic voltage: 14-18V
Electrode area: 100 cm ² / Current density per electrode surface: 0.5 A / cm ²

1 single wafer cleaning machine 4 sulfuric acid drainage tank 7 cooler 8 storage tank 10 cooler 14 catholyte storage tank 17a ultrapure water supply line 17b concentrated sulfuric acid supply line 18a ultrapure water supply line 18b concentrated sulfuric acid supply line 20 electrolyzer 24 Diaphragm 25 Diaphragm 26a Anode chamber 26b Cathode chamber 27a Anode chamber 27b Cathode chamber 30a Return tube 30b Return tube 31a Feed tube 31b Feed tube 32 Return tube 33 Feed tube 100 Semiconductor substrate

Claims (2)

In a sulfuric acid electrolysis method in which sulfuric acid is used for the catholyte and anolyte of a diaphragm type electrolysis cell comprising an anode and a cathode composed of diamond electrodes ,
When the sulfuric acid concentration of the anolyte is 80 to less than 96% by mass , the liquid flow rate in the anode chamber and the cathode chamber is 10 m / h or more , and the electrolytic current density is 0.1 to 1.0 A / cm ² , A sulfuric acid electrolysis method, wherein the sulfuric acid concentration of the catholyte is 10 to 50% by mass, the liquid temperatures of the anolyte and the catholyte are 40 to 70 ° C., and used for 10 hours or more .   The sulfuric acid electrolysis method according to claim 1, wherein the diaphragm provided in the diaphragm type electrolytic cell is a fluororesin cation exchange membrane.

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