JP5592611B2 - Persulfuric acid production apparatus and persulfuric acid production method - Google Patents

Description

  The present invention relates to an apparatus and a method for producing persulfuric acid dissolved water useful as an oxidizing agent or the like by an electrochemical technique.

  Wafer cleaning in the VLSI manufacturing process is a process for stripping and cleaning resist residues, fine particles, metals, natural oxide films, etc. For example, ozone gas is blown into concentrated sulfuric acid / hydrogen peroxide mixed solution (SPM) or concentrated sulfuric acid. A method of cleaning a wafer using a solution (SOM) or the like is often used. Thus, when hydrogen peroxide or ozone is added to (high concentration) sulfuric acid, the sulfuric acid is oxidized to produce persulfuric acid. And it is known that persulfuric acid is useful for cleaning the wafer and the like because it generates a strong oxidizing power when self-decomposing.

  In the cleaning method using SPM, the generated persulfuric acid is reduced in oxidizing power with use due to autolysis or the like. For this reason, it is necessary to repeatedly supply hydrogen peroxide water during cleaning. Further, when hydrogen peroxide solution is replenished, the sulfuric acid concentration in the SPM is reduced. Therefore, when the sulfuric acid concentration falls below a predetermined concentration, it is necessary to replace it with new high-concentration sulfuric acid.

  In the cleaning method using SPM, the amount of persulfuric acid generated by adding high-concentration sulfuric acid that has filled the cleaning tank once and hydrogen peroxide water several times is small. Further, in the cleaning method using SOM, the generation efficiency of persulfuric acid with respect to the ozone blowing amount is very low. Therefore, in these methods, since the concentration of persulfuric acid produced is limited, the cleaning effect is also limited.

  As a method for producing persulfuric acid, in addition to the above method, a method for producing persulfuric acid by electrolyzing a sulfuric acid solution is known (for example, see Patent Documents 1 to 4). Such an electrochemical method can increase the concentration of persulfuric acid as compared with the above method, and can also reduce the amount of chemicals used.

JP 2001-192874 A Special table 2003-511555 gazette JP 2006-111943 A JP 2008-19507 A

  Incidentally, in order to enhance the peeling effect of the resist film formed on the wafer, it is desired that not only the persulfuric acid concentration but also the sulfuric acid concentration is high. However, the conventional electrochemical method as described above has a problem that current efficiency for producing persulfuric acid decreases when the sulfuric acid concentration is high. As electrolysis conditions, it is necessary to perform electrolysis at a low temperature in order to suppress the self-decomposition of persulfuric acid due to heat.

  Accordingly, an object of the present invention is to provide a persulfuric acid production apparatus and a persulfuric acid production method capable of producing persulfuric acid-dissolved water in which sulfuric acid and persulfuric acid coexist at a high concentration.

The present invention is an apparatus for producing persulfuric acid comprising an anode and a cathode, wherein a current is passed between the anode and the cathode, and a sulfuric acid-containing solution is electrolyzed to produce persulfuric acid-dissolved water, the anode side the concentration of sulfuric acid supplied solution is in the range of 92 to 96 wt%, when the electrolysis of the sulfuric acid-containing solution, a predetermined control unit Ru is stopped at intervals the current flowing between the anode and the cathode It is to be prepared.

Further, in the above persulfate manufacturing apparatus, the stop time of the currents by the control means is preferably in the range of 10 seconds to 10 minutes.

The present invention is also a persulfuric acid production method for producing persulfuric acid-dissolved water by passing an electric current between an anode and a cathode and electrolyzing a sulfuric acid-containing solution, wherein the sulfuric acid in the solution supplied to the anode side the concentration is in the range of 92 to 96 wt%, when the electrolysis of the sulfuric acid-containing solution, is the also you stopped at a predetermined interval a current flowing between the anode and the cathode.

  According to the present invention, it is possible to produce persulfuric acid-dissolved water in which sulfuric acid and persulfuric acid coexist at a high concentration.

It is a schematic diagram which shows an example of a structure of the persulfuric acid manufacturing apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the electricity supply pattern of this embodiment. It is a diagram showing the relationship between the current amount and the persulfate (H ₂ S ₂ O ₈₎ concentration and the voltage in Example 1 and Comparative Example 1. It is a diagram showing the relationship between the current amount and the persulfate (H ₂ S ₂ O ₈₎ concentration and the voltage in the second embodiment. It is a diagram showing the relationship between the current amount and the persulfate (H ₂ S ₂ O ₈₎ concentration and the voltage in Example 3 and Comparative Example 2. It is a diagram showing the relationship between the current amount and the persulfate (H ₂ S ₂ O ₈₎ concentration and the voltage in Example 4 and Comparative Example 3.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  FIG. 1 is a schematic diagram showing an example of the configuration of a persulfuric acid production apparatus according to an embodiment of the present invention. As shown in FIG. 1, the persulfuric acid production apparatus 1 includes an electrolytic cell 10, an anolyte tank 12, an anolyte pump 14, an anolyte supply line 16, a persulfate discharge line 18, a catholyte tank 20, a catholyte pump 22, A catholyte supply line 24 and a catholyte discharge line 26 are provided.

  The electrolytic cell 10 includes a diaphragm 28 such as an ion exchange membrane, an anode 30, and a cathode 32. The electrolytic cell 10 is partitioned into an anode chamber 34 and a cathode chamber 36 by a diaphragm 28. The anode 30 is disposed in the anode chamber 34, and the cathode 32 is disposed in the cathode chamber 36. The anode 30 and the cathode 32 are connected to the power supply 40 via a controller 38 (control means) outside the electrolytic cell 10 by conducting wires.

  An anolyte inlet and an anolyte outlet are provided on the anode chamber 34 side of the electrolytic cell 10. The anolyte inlet of the electrolytic cell 10 and the anolyte tank 12 are connected by an anolyte supply line 16. The anolyte supply line 16 is provided with an anolyte pump 14. A persulfuric acid discharge line 18 is connected to the anolyte outlet of the electrolytic cell 10. On the other hand, the cathode chamber 36 side of the electrolytic cell 10 is provided with a catholyte inlet and a catholyte outlet. The catholyte inlet of the electrolytic cell 10 and the catholyte tank 20 are connected by a catholyte supply line 24. The catholyte supply line 24 is provided with a catholyte pump 22. A catholyte discharge line 26 is connected to the catholyte outlet of the electrolytic cell 10. In this embodiment, the persulfuric acid discharge line 18 is branched so that a part of the anolyte circulates, the branch line 18a is connected to the anolyte tank 12, and the catholyte circulates. A catholyte discharge line 26 is connected to the catholyte tank 20.

  Below, operation | movement of the persulfuric acid manufacturing apparatus 1 which concerns on this embodiment is demonstrated.

  First, the anolyte pump 14 is operated, and the anolyte is supplied from the anolyte tank 12 through the anolyte supply line 16 to the anode chamber 34 of the electrolytic cell 10. Further, the catholyte pump 22 is operated, and the catholyte is supplied from the catholyte tank 20 through the catholyte supply line 24 to the cathode chamber 36 of the electrolytic cell 10. Here, a sulfuric acid-containing solution is used for the anode 30 liquid and the cathode 32 liquid. Thereafter, when a positive voltage is applied from the power source 40 to the anode 30 and a negative voltage is applied to the cathode 32, and a current is passed between the anode 30 and the cathode 32, the following reaction mainly occurs in the anode chamber 34.

^{_{2SO 4 2- → S 2 O 8}} 2- + 2e - (1)
2HSO ₄ ⁻ → S ₂ O ₈ ²⁻ + 2H ⁺ + 2e ⁻ (2)
HSO ₄ ⁻ + H ₂ O → HSO ₅ ⁻ + 2H ⁺ + 2e ⁻ (3)

Further, in the cathode chamber 36, the following reaction mainly occurs.
_{^{2H + + 2e - → H 2}} ↑

By electrolyzing the sulfuric acid-containing solution in this way, persulfuric acid-dissolved water containing persulfuric acid such as peroxomonosulfuric acid (H ₂ SO ₅ ) and peroxodisulfuric acid (H ₂ S ₂ O ₈ ) can be obtained. The persulfuric acid-dissolved water passes through the persulfuric acid discharge line 18 and is used for cleaning wafers and the like. A part of the persulfuric acid-dissolved water is returned to the anolyte tank 12 through the branch line 18a. On the other hand, the catholyte that has passed through the cathode chamber 36 passes through the catholyte discharge line 26 and is returned to the catholyte tank 20.

In the case of electrolyzing high-concentration sulfuric acid, normally, when a positive voltage is applied to the anode 30 and a negative voltage is applied to the cathode 32 and a current is continuously applied between the anode 30 and the cathode 32, the electrolysis voltage rises and persulfuric acid is generated. Therefore, the current efficiency is reduced, and the amount of persulfuric acid produced is reduced. In particular, this is likely to occur when the energization amount is high and the sulfuric acid concentration of the sulfuric acid-containing solution supplied to the anode chamber 34 is higher. This is because the persulfate ions (HSO ₅ ⁻ , S ₂ O ₈ ²⁻ ) generated by continuing to pass a current between the anode 30 and the cathode 32 remain in the vicinity of the anode 30, so that new sulfate ions (and This is probably because sulfite ions are less likely to diffuse (or adsorb) near the anode 30. Therefore, in the present embodiment, the generated persulfate ions are separated from the vicinity of the anode 30 by stopping the current flowing between the anode 30 and the cathode 32 at a predetermined interval or by applying a reverse current, and the reduced sulfate ions. The diffusivity (adsorbability) is restored, and the decrease in current efficiency due to persulfuric acid generation due to voltage increase is suppressed.

  FIG. 2 is a diagram illustrating an example of the energization pattern of the present embodiment. FIG. 2A shows an energization pattern in which energization and stopping between the anode 30 and the cathode 32 are repeated. In FIG. 2B, a positive voltage is applied to the anode 30 and a negative voltage is applied to the cathode 32, a negative voltage is applied to the anode 30 and a positive voltage is applied to the cathode 32, and a positive current and a reverse current are applied between the anode 30 and the cathode 32. Is an energization pattern in which is repeatedly performed. Such control is performed by storing the energization pattern as described above in the controller 38 shown in FIG.

Here, the time for stopping the current or the time for flowing the reverse current (t ₂ shown in FIGS. 2A and 2B) is the amount of electrolysis on the anode 30 side, the sulfuric acid concentration of the sulfuric acid-containing solution supplied to the anode 30 side, etc. However, when the amount of electrolysis during the stop or flow of the reverse current is in the range of 0.1 to 5 Ah / L, for example, the stop time of the current or the time of flowing the reverse current Is preferably in the range of 10 seconds to 10 minutes. If the current stop time or the reverse current flow time is less than 10 seconds, it becomes difficult to recover the reduced diffusibility (adsorbability) of sulfate ions in the vicinity of the anode 30, and if it exceeds 10 minutes, The amount of persulfuric acid generated from the 30th side may decrease, and the peeling effect of the resist film formed on the wafer may decrease. Moreover, it is preferable to make the time (( ₁ ) shown to FIG. 2 (A) and (B)) to flow the (positive) electric current longer than the electric current stop time or the time to flow a reverse current, for example, 1 minute to 30 It is preferably in the range of minutes.

  The sulfuric acid concentration of the sulfuric acid-containing solution as the anolyte used in the present embodiment is preferably in the range of 92 to 96% by weight. When the concentration of the sulfuric acid solution is less than 92% by weight, the amount of persulfuric acid generated increases, but the concentration of sulfuric acid in the persulfuric acid-dissolved water obtained by the electrolysis method of the present embodiment decreases, and the resist film formed on the wafer The peeling effect may be reduced. If the sulfuric acid concentration is more than 96% by weight, a sufficient amount of persulfuric acid may not be generated even by the electrolysis method of this embodiment. Further, the temperature of the sulfuric acid-containing solution as the anolyte is preferably 80 ° C. or less, more preferably 60 ° C. or less, in that it can suppress the self-decomposition of persulfuric acid obtained by the electrolysis method of this embodiment. Even more preferred is less than or equal to ° C. The method for controlling the temperature of the sulfuric acid-containing solution is not particularly limited. For example, it is performed by installing a heater in the anolyte tank 12 or installing a cooler in the anolyte supply line 16.

  The catholyte used in the present embodiment may be the same sulfuric acid-containing solution as the anolyte or a solution in which a conductive substance different from the anolyte is dissolved. In addition, when a sulfuric acid-containing solution is used as the catholyte, it is preferable to use a sulfuric acid-containing solution having a concentration similar to that of the sulfuric acid-containing solution as the anolyte, in that more persulfuric acid can be generated. It may be a sulfuric acid-containing solution having a concentration lower than the sulfuric acid concentration of the anolyte, for example, 10% by weight or less.

The electrolytic cell 10 used in this embodiment may be a two-chamber electrolytic cell partitioned into an anode chamber 34 and a cathode chamber 36 by a diaphragm 28 as shown in FIG. Good. However, in the diaphragm-type electrolytic cell, persulfate ions such as peroxomonosulfate ions (HSO ₅ ⁻ ) and peroxodisulfate ions (S ₂ O ₈ ²⁻ ) once generated at the anode 30 come into contact with the cathode 32 and sulfuric acid. Since there is a possibility of being reduced to ions, it is preferable to use a two-chamber electrolytic cell. Further, the electrolytic cell 10 is not particularly limited to a single electrode type or a bipolar type.

  As the diaphragm 28 used in the present embodiment, for example, a neutral membrane such as a trade name Poreflon or a cation exchange membrane such as a trade name Nafion, Aciplex, Flemion or the like can be used. However, in terms of corrosion resistance, a cation exchange membrane is used. It is preferable to use it.

  As the anode 30 and the cathode 32 used in the present embodiment, for example, platinum, a diamond-coated electrode or the like is used, but the cathode 32 can also be a carbon, titanium, niobium, tantalum, zirconium electrode or the like. When the sulfuric acid-containing solution supplied to the cathode 32 side can be reduced in concentration by having the diaphragm 28, carbon, titanium, niobium, tantalum, zirconium electrodes, etc. should be used rather than platinum, diamond-coated electrodes, etc. However, it is preferable in terms of corrosion resistance and cost.

The distance between the anode 30 and the cathode 32 is not particularly limited, but is preferably shorter. This is because by shortening the distance between the anode 30 and the cathode 32, generation of Joule heat due to solution resistance can be suppressed, and self-decomposition of the generated persulfuric acid can be suppressed. The distance between the anode 30 and the cathode 32 is preferably in the range of 1 to 100 mm, for example. The current density between the anode 30 and the cathode 32 is not particularly limited, but is preferably in the range of 10 to 2000 mA / cm ² , for example.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

(Examples 1 and 2)
Using the persulfuric acid production apparatus shown in FIG. 1, the sulfuric acid solution was electrolyzed under the following conditions to produce persulfuric acid-dissolved water. A 96 wt% sulfuric acid solution (60 ° C. or lower) was used as the anolyte, and a 1 mol / L sulfuric acid solution (60 ° C. or lower) was used as the catholyte. The anode used in the persulfuric acid production apparatus was a diamond-coated electrode, and the cathode was a zirconium electrode. The electrolysis conditions of Example 1 were energized for 240 seconds and then stopped for 60 seconds as one cycle, and this was repeated, and the electrolysis conditions of Example 2 were energized for 290 seconds and then stopped for 10 seconds as one cycle. I decided to repeat it.

(Comparative Example 1)
In Comparative Example 1, persulfuric acid-dissolved water was produced under the same conditions as in Example 1 except that the sulfuric acid solution was electrolyzed between the anode and the cathode at all times.

(Example 3)
In Example 3, persulfuric acid-dissolved water was produced by electrolyzing the sulfuric acid solution under the same conditions as in Example 1, except that a sulfuric acid solution having a concentration of 92% by weight (60 ° C. or lower) was used as the anolyte.

(Comparative Example 2)
In Comparative Example 2, the same conditions as in Example 3 (sulfuric acid solution having a concentration of 92 wt% in the anolyte (60 ° C. or lower)) except that the sulfuric acid solution was electrolyzed between the anode and the cathode at all times, The sulfuric acid solution was electrolyzed to produce persulfuric acid-dissolved water.

Example 4
In Example 4, persulfuric acid-dissolved water was produced by electrolyzing the sulfuric acid solution under the same conditions as in Example 1 except that a 85 wt% sulfuric acid solution (60 ° C. or lower) was used as the anolyte.

(Comparative Example 3)
In Comparative Example 3, the same conditions as in Example 4 (85% by weight sulfuric acid solution (60 ° C. or lower) in the anolyte) except that the sulfuric acid solution was electrolyzed between the anode and the cathode at all times, The sulfuric acid solution was electrolyzed to produce persulfuric acid-dissolved water.

Table 1 summarizes the current efficiencies of Examples 1 and 2 and Comparative Example 1 when the energization amount is 10 Ah / L. FIG. 3 summarizes the relationship between the energization amount, the persulfuric acid (H ₂ S ₂ O ₈ ) concentration, and the voltage in Example 1 and Comparative Example 1. FIG. 4 summarizes the relationship between the energization amount, the persulfuric acid (H ₂ S ₂ O ₈ ) concentration, and the voltage in Example 2. Table 2 summarizes the current efficiencies of Example 3 and Comparative Example 2 at an energization amount of 10 Ah / L. FIG. 5 summarizes the relationship between the amount of energization, the concentration of persulfuric acid (H ₂ S ₂ O ₈ ), and the voltage in Example 3 and Comparative Example 2. Table 3 summarizes the current efficiencies of Example 4 and Comparative Example 3 at an energization amount of 10 Ah / L. FIG. 6 summarizes the relationship between the amount of energization, the concentration of persulfuric acid (H ₂ S ₂ O ₈ ), and the voltage in Example 4 and Comparative Example 3.

  As can be seen from Table 1, when the sulfuric acid concentration of the anolyte is 96% by weight, the current efficiency when the energization amount is 10 Ah / L is that of Examples 1 and 2 in which the energization-stop was repeated from Comparative Example 1 in which the energization was always conducted. Showed a higher value. Further, as can be seen from FIG. 3, when the sulfuric acid concentration of the anolyte is 96% by weight, in Comparative Example 1 in which energization was always performed, when the energization amount was 5 Ah / L or more, the electrolysis voltage increased and the persulfuric acid concentration Was also almost constant. On the other hand, in Example 1 in which energization for 240 seconds and stop for 60 seconds was repeated, the electrolysis voltage did not increase even when the energization amount increased, and the persulfuric acid concentration increased in proportion to the increase in the energization amount. . Further, as can be seen from FIG. 4, in Example 2 in which 290 seconds energization-10 seconds stop was repeated, the electrolysis voltage did not increase even when the energization amount increased, and exceeded the increase in the energization amount. The sulfuric acid concentration also increased. That is, it has been found that even if the energization-stop time is changed, the increase in the electrolysis voltage due to the increase in the energization amount can be suppressed, and the persulfuric acid concentration can be increased in proportion to the increase in the energization amount.

  In addition, as can be seen from Table 2, when the sulfuric acid concentration of the anolyte is 92% by weight, the current efficiency when the energization amount is 10 Ah / L is Example 3 in which the energization-stop was repeated compared with Comparative Example 2 in which the energization was always conducted. Showed a higher value. Further, as can be seen from FIG. 5, when the sulfuric acid concentration of the anolyte was 92% by weight, in Comparative Example 2 in which energization was always performed, the electrolysis voltage increased when the energization amount was 13 Ah / L or more, In Example 3 in which the energization for 240 seconds and the stop for 60 seconds were repeated, the electrolytic voltage did not increase even when the energization amount was 13 Ah / L or more. In Comparative Example 2, the persulfuric acid concentration increased with an increase in the energization amount, but the increase rate decreased. On the other hand, in Example 3, the increase rate of the persulfuric acid concentration hardly decreased even when the energization amount was increased.

  As can be seen from Table 3, when the sulfuric acid concentration of the anolyte is 85% by weight, the current efficiency when the energization amount is 10 Ah / L is the comparative example 3 in which the energization was always conducted and the example in which the energization-stop was repeated. All four values were almost the same. Further, as can be seen from FIG. 6, when the sulfuric acid concentration of the anolyte is 85% by weight, the behavior of the electrolysis voltage and the increasing tendency of the persulfuric acid concentration accompanying the increase in the amount of energization are the comparative example 3 in which the energization was always conducted. In Example 4 in which the energization for 240 seconds and the stop for 60 seconds were repeated, the results were almost the same.

  Moreover, about Example 1,3,4, it replaced with the electrolysis condition of 240 second positive current-60 second reverse current from the electrolysis condition of energization-stop, and it tested. As a result, it was confirmed that the same result as the electrolysis condition of energization-stop was obtained even under the electrolysis conditions of positive current-reverse current. From the above, in the apparatus of this embodiment that produces persulfuric acid under electrolysis conditions that repeat energization-stop or positive current-reverse current, even when the sulfuric acid concentration of the anolyte is low, it is always energized to produce persulfuric acid. In addition, when the sulfuric acid concentration of the anolyte is high, the voltage rise due to the increase in the amount of current flow is suppressed and the persulfuric acid It was found that the production amount can be increased.

  DESCRIPTION OF SYMBOLS 1 Persulfuric acid production apparatus, 10 Electrolyzer, 12 Anolyte tank, 14 Anolyte pump, 16 Anolyte supply line, 18 Persulfate discharge line, 18a Branch line, 20 Catholyte tank, 22 Catholyte pump, 24 Catholyte supply Line, 26 catholyte discharge line, 28 diaphragm, 30 anode, 32 cathode, 34 anode chamber, 36 cathode chamber, 38 controller, 40 power supply.

Claims (2)

A persulfuric acid production apparatus comprising an anode and a cathode, passing an electric current between the anode and the cathode, electrolyzing a sulfuric acid-containing solution, and producing persulfuric acid-dissolved water,
The sulfuric acid concentration in the solution supplied to the anode side is in the range of 92 to 96% by weight, and during the electrolysis of the sulfuric acid-containing solution, the sulfuric acid-containing solution is supplied to the anode side and the sulfuric acid-containing material is supplied to the cathode side. Control means for stopping the current flowing between the anode and the cathode at a predetermined interval while supplying the solution or the conductive substance dissolving solution ,
The apparatus for producing persulfuric acid , wherein the current stop time by the control means is in a range of 10 seconds to 10 minutes, and the current supply time by the control means is longer than the current stop time . A persulfuric acid production method for producing persulfuric acid-dissolved water by passing an electric current between an anode and a cathode, electrolyzing a sulfuric acid-containing solution,
The sulfuric acid concentration in the solution supplied to the anode side is in the range of 92 to 96% by weight, and during the electrolysis of the sulfuric acid-containing solution, the sulfuric acid-containing solution is supplied to the anode side and the sulfuric acid-containing material is supplied to the cathode side. While supplying the solution or the conductive substance dissolving solution, the current flowing between the anode and the cathode is stopped at a predetermined interval ,
A method for producing persulfuric acid , wherein the current stop time is in the range of 10 seconds to 10 minutes, and the current supply time is longer than the current stop time .

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