JP2016167560A - Production method of electrolytic sulfuric acid solution and production apparatus of electrolytic sulfuric acid solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce electrolytic sulfuric acid solution using a sulfuric acid solution efficiently.SOLUTION: In a production method of an electrolytic sulfuric acid solution using a primary sulfuric acid solution of relatively low sulfuric acid concentration, and a secondary sulfuric acid solution of relatively high sulfuric acid concentration, a primary electrolytic sulfuric acid solution is produced by decomposing the primary sulfuric acid solution electrolytically, a secondary electrolytic sulfuric acid solution where the sulfuric acid concentration was adjusted to a predetermined concentration is produced by admixing the secondary sulfuric acid solution to the primary electrolytic sulfuric acid solution, and then the secondary electrolytic sulfuric acid solution is decomposed electrolytically while being circulated between the utilization side.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a technique for producing an electrolytic sulfuric acid solution used as a cleaning liquid or the like for removing an object to be removed from an electronic material such as a silicon wafer.

Conventionally, a process called SPM in which concentrated sulfuric acid and hydrogen peroxide solution are mixed is used in a process of removing a resist, an unnecessary metal, or the like to be removed from an electronic material such as a silicon wafer. Since this method 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.
On the other hand, the inventors have already developed a cleaning method and a cleaning system in which sulfuric acid is circulated using an electrolytic sulfuric acid solution containing an oxidizing substance such as persulfuric acid obtained by electrolyzing sulfuric acid as a cleaning solution. (For example, see Patent Documents 1 to 3). In this cleaning system, it is possible to obtain a high cleaning effect while reducing the amount of chemical liquid used and the amount of waste liquid.
In addition, there has been proposed a method in which an electrolyzed sulfuric acid solution is always mixed with another sulfuric acid solution to obtain a high-temperature sulfuric acid solution heated by mixing heat and used for cleaning (see, for example, Patent Documents 4 and 5).

JP 2006-114880 A JP 2006-278687A JP 2008-1111184 A JP 2008-066644 A JP 2008-095144 A

Collection Czechoslov. Chem. Commun. Jan Balej et al., Vol. 44, PP. 1510-1520, 1979

  On the other hand, in the cleaning system disclosed in the above-mentioned patent document, it is necessary to apply the solution to the entire system while adjusting the sulfuric acid stock solution of about 96% by mass to a sulfuric acid concentration of about 80 to 92% by mass, and then perform electrolysis Therefore, there is a drawback that it takes time from the start of the cleaning system, that is, from the liquid adjustment to the start of cleaning of the wafer. The start-up of the cleaning system herein includes restarting after replacement of the solution in the system.

  The present invention has been made against the background of the above circumstances, and an object thereof is to provide an electrolytic sulfuric acid solution manufacturing method and an electrolytic sulfuric acid solution manufacturing apparatus that can quickly start up the supply of the electrolytic sulfuric acid solution.

Of the methods for producing an electrolytic sulfuric acid solution of the present invention, the first present invention comprises:
A method for producing an electrolytic sulfuric acid solution using a primary sulfuric acid solution and a secondary sulfuric acid solution having a relatively high sulfuric acid concentration relative to the primary sulfuric acid solution,
The primary sulfuric acid solution is electrolyzed to form a primary electrolytic sulfuric acid solution, and the secondary sulfuric acid solution is mixed with the primary electrolytic sulfuric acid solution to adjust the sulfuric acid concentration to a predetermined concentration. A sulfuric acid solution is generated, and the electrolysis is performed while circulating the sulfuric acid solution between the sulfuric acid electrolysis cell and the sulfuric acid solution storage tank.

  The method for producing an electrolytic sulfuric acid solution according to a second aspect of the present invention is the method according to the first aspect, wherein the sulfuric acid concentration of the primary electrolytic sulfuric acid solution is in the range of 30% by mass to 50% by mass. The sulfuric acid concentration is in the range of 80% by mass to 92% by mass.

  The method for producing an electrolytic sulfuric acid solution according to the third aspect of the present invention is characterized in that, in the first or second aspect of the present invention, at least an anode surface of the electrodes used for electrolysis is a conductive diamond.

  According to a fourth aspect of the present invention, there is provided a method for producing an electrolytic sulfuric acid solution according to any one of the first to third aspects of the present invention, wherein the secondary electrolytic sulfuric acid solution is circulated between the secondary electrolytic sulfuric acid solution and the use side. It is characterized by performing electrolysis.

  A method for producing an electrolytic sulfuric acid solution according to a fifth aspect of the present invention is the cleaning process according to any one of the first to third aspects, wherein the use side removes an object to be removed that has become unnecessary in the production process from the electronic material. It is a facility.

  A method for producing an electrolytic sulfuric acid solution according to a sixth aspect of the present invention is the method according to any one of the first to fifth aspects, wherein the secondary electrolytic sulfuric acid solution is prepared by mixing the secondary sulfuric acid solution with the primary electrolytic sulfuric acid solution. The secondary electrolytic sulfuric acid solution is spread between the use side and then the secondary electrolytic sulfuric acid solution is electrolyzed along with the use of the secondary electrolytic sulfuric acid solution on the usage side. To do.

  A method for producing an electrolytic sulfuric acid solution according to a seventh aspect of the present invention is the method according to any one of the first to sixth aspects, wherein the secondary electrolytic sulfuric acid solution is obtained by mixing the secondary electrolytic sulfuric acid solution with the primary electrolytic sulfuric acid solution. Then, the secondary electrolytic sulfuric acid solution is electrolyzed.

  The method for producing an electrolytic sulfuric acid solution according to an eighth aspect of the present invention is the secondary electrolytic sulfuric acid solution sent to the use side in the electrolysis of the secondary electrolytic sulfuric acid solution according to any one of the first to seventh aspects of the present invention. Is collected and used for the electrolysis.

The ninth aspect of the electrolytic sulfuric acid solution production apparatus of the present invention is:
A sulfuric acid electrolysis cell;
An electrolyte reservoir,
An electrolytic circulation path for circulating a solution between the sulfuric acid electrolysis cell and the electrolytic solution storage tank; and an electrolytic solution supply path for supplying a solution from the electrolytic solution storage tank to a use facility of electrolytic sulfuric acid, A primary sulfuric acid solution supply unit for supplying a sulfuric acid solution to the electrolytic solution storage tank, and a secondary sulfuric acid for supplying a sulfuric acid solution having a relatively high sulfuric acid concentration to the sulfuric acid solution supplied from the primary sulfuric acid solution supply unit A solution supply unit is connected, and the primary sulfuric acid solution supply unit and the secondary sulfuric acid solution supply unit can switch the solution supply to the electrolyte storage tank. .

The electrolytic sulfuric acid solution manufacturing apparatus of the tenth aspect of the present invention is the ninth aspect of the invention,
The primary sulfuric acid solution supply unit includes a secondary sulfuric acid solution supply unit and a pure water supply unit, and the secondary sulfuric acid solution and pure water are supplied and mixed in a pipe or in a storage tank to a predetermined concentration. A primary sulfuric acid solution is prepared to be prepared.

  Below, the content prescribed | regulated by this invention is demonstrated.

Sulfuric acid concentration of primary electrolytic sulfuric acid solution: 30% by mass to 50% by mass
Sulfuric acid concentration of secondary electrolytic sulfuric acid solution: 80% by mass to 92% by mass
The secondary electrolytic sulfuric acid solution has a higher sulfuric acid concentration than the primary electrolytic (primary) sulfuric acid solution.
The present invention relates to an electrolytic sulfuric acid manufacturing technique using an electrolytic sulfuric acid solution obtained by electrolyzing sulfuric acid as a cleaning solution, etc., and electrolyzing the sulfuric acid solution under a sulfuric acid concentration condition capable of generating an oxidizing substance with high efficiency, and thereafter By adjusting to the sulfuric acid concentration, the production time of electrolytic sulfuric acid having a desired liquid quality can be shortened, and the start-up time of the cleaning system or the like can be shortened. The sulfuric acid solution is mainly composed of sulfuric acid, but may also contain salt ions or other ions.

When sulfuric acid is electrolyzed, peroxodisulfuric acid is produced according to the following reaction formula (1).
2HSO ₄ ⁻ → H ₂ S ₂ O ₈ + 2e ⁻ (1)
Further, peroxomonosulfuric acid is produced from peroxodisulfuric acid by the equilibrium reaction shown in the formula (2), and further hydrogen peroxide is produced by the equilibrium reaction shown in the formula (3). Therefore, an oxidizing substance such as peroxodisulfuric acid, peroxomonosulfuric acid (herein, peroxodisulfuric acid and peroxomonosulfuric acid are collectively referred to as persulfuric acid), and hydrogen peroxide are mixed in the sulfuric acid electrolyte. Each of these has a strong oxidizing power, and can oxidize and decompose resist on the wafer that is no longer necessary in the semiconductor manufacturing process.
H ₂ S ₂ O ₈ + H ₂ O _→ ^← H ₂ SO ₅ + H ₂ SO ₄ (2)
H ₂ SO ₅ + H ₂ O _→ ^← H ₂ O ₂ + H ₂ SO ₄ (3)

  It has long been known that the concentration of sulfuric acid greatly affects the current efficiency in the production of persulfuric acid in the reaction of electrolyzing sulfuric acid to produce persulfuric acid. Jan Balej et al., Using a Pt electrode, showed that 7-8 M (about 50-55 mass%) had the highest persulfuric acid production efficiency at a sulfuric acid concentration of 1-13 M (see Non-Patent Document 1). Similarly, in the electrolysis reaction using a conductive diamond electrode, the sulfuric acid concentration greatly affects the persulfuric acid production efficiency, and the highest efficiency is obtained when electrolysis is performed at a sulfuric acid concentration of 40 to 50% by mass at an electrolyte temperature of 30 to 50 ° C.

On the other hand, it is desirable that the concentration of sulfuric acid serving as a solvent is 80% by mass or more in order to exhibit sulfuric acid oxidizing ability such as a resist stripping step. When electrolysis is performed at this concentration, the production efficiency of persulfuric acid is greatly reduced. Therefore, when starting up the cleaning system, instead of electrolyzing after adding sulfuric acid adjusted to 80 to 92% by mass, sulfuric acid having a high persulfuric acid production efficiency is adjusted and electrolyzed. The start-up time can be shortened by adding an oxidizing agent such as sulfuric acid and then adjusting the sulfuric acid concentration as a solvent to, for example, 80 to 92% by mass with a sulfuric acid stock solution of about 96% by mass.
Note that the electrode used here is a conductive diamond electrode at least on the anode surface. The conductive diamond electrode has higher persulfuric acid generation efficiency than noble metal-based electrodes such as Pt, and the metal does not elute on the solution side. Therefore, the obtained sulfuric acid electrolyte is used in a process of washing electronic materials. Suitable for cleaning liquid.

  As described above, according to the present invention, the production time of the target electrolytic sulfuric acid solution can be shortened.

It is the schematic which shows the batch type sulfuric acid recycle type cleaning system of one embodiment of the present invention. It is the schematic which shows Embodiment 2 which is a modification of the batch-type sulfuric acid recycle type cleaning system of embodiment of FIG. It is the schematic which shows the single-wafer | sheet-fed sulfuric acid recycle type cleaning system of Embodiment 3 of this invention. It is the schematic which shows Embodiment 4 which is a modification of the single-wafer | sheet-fed sulfuric acid recycle type cleaning system of embodiment of FIG. Similarly, it is a flowchart which shows the procedure of a washing | cleaning system. It is a graph which shows the relationship between a sulfuric acid density | concentration and an oxidizing agent density | concentration.

(Embodiment 1)
Next, a batch type sulfuric acid recycle type cleaning system including an electrolytic sulfuric acid solution manufacturing apparatus according to an embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1, the batch type sulfuric acid recycling type cleaning system has an electrolytic cell 2, a sulfuric acid solution storage tank 3, and a batch type cleaning tank 10.
The electrolytic cell 2 is connected to the sulfuric acid solution storage tank 3 by a feed circulation line 4A and a return circulation line 4B. The feed circulation line 4A is connected to the liquid inlet side of the electrolysis cell 2 via the pump 5 and the cooler 6 in the feed direction from the sulfuric acid solution storage tank 3 to the electrolysis cell 2, and is discharged from the electrolysis cell 2. The return circulation line 4B is connected to the side. Thereby, the sulfuric acid solution can be passed through the electrolytic cell 2. The feed circulation line 4A and the return circulation line 4B correspond to the electrolytic circuit of the present invention.

The electrolysis cell 2 has an anode 2A and a cathode 2B, and is configured such that a sulfuric acid solution is passed between both electrodes. In addition to the anode 2A and the cathode 2B, a bipolar electrode may be provided. As for an electrode, it is desirable that at least an anode surface of the electrode surface is made of conductive diamond.
The sulfuric acid solution storage tank 3, the feed circulation line 4 </ b> A, the return circulation line 4 </ b> B, the electrolytic cell 2, the pump 5, and the cooler 6 constitute the electrolytic sulfuric acid device 1.

The sulfuric acid solution storage tank 3 is connected to a batch type cleaning tank 10 in which the electronic material 100 such as a semiconductor wafer is cleaned by a feed circulation line 11A and a return circulation line 11B. The batch-type cleaning tank 10 corresponds to the use side facility in the present invention.
In the feed circulation line 11 </ b> A, a pump 12 and a filter 13 are sequentially provided in the feed direction from the sulfuric acid solution storage tank 3 to the batch type washing tank 10. The return circulation line 11B is sequentially provided with a pump 14 and a cooler 15 in the feed direction from the batch type washing tank 10 to the sulfuric acid solution storage tank 3.
The feed circulation line 11A corresponds to the electrolytic solution supply path of the present invention.

  In the return circulation line 11B, the branch path 11C is branched downstream of the pump 14 and upstream of the cooler 15, and the downstream side of the branch path 11C joins the feed circulation line 11A downstream of the filter 13. . In the branch path 11C, a heater 16 and a filter 17 are sequentially provided from the return circulation line 11B side toward the feed circulation line 11A side.

Also, a pure water supply line 7, a primary concentrated sulfuric acid supply line 8A, and a secondary concentrated sulfuric acid supply line 8B are connected to the sulfuric acid solution storage tank 3 in which the sulfuric acid solution is stored. The primary concentrated sulfuric acid supply line 8A corresponds to a primary sulfuric acid solution supply unit, and the secondary concentrated sulfuric acid supply line 8B corresponds to a secondary sulfuric acid solution supply unit. The concentrated sulfuric acid supply line 8A for the primary and the concentrated sulfuric acid supply line 8B for the secondary can supply concentrated sulfuric acid having different sulfuric acid concentrations to the sulfuric acid solution storage tank 3 by switching the supply. Note that the concentrated sulfuric acid supply line 8A for primary use and the concentrated sulfuric acid supply line 8B for secondary use may be shared by one line, and concentrated sulfuric acid having different sulfuric acid concentrations may be switched and supplied.
When adjusting the concentration by adding pure water from the pure water supply line 7 to the sulfuric acid solution supplied from the primary concentrated sulfuric acid line 8A or the secondary concentrated sulfuric acid supply line 8B, the primary concentrated sulfuric acid line 8A The pure water supply line 7 constitutes a primary sulfuric acid solution supply unit, and the secondary concentrated sulfuric acid supply line 8B and the pure water supply line 7 constitute a secondary sulfuric acid solution supply unit.

  Furthermore, in this embodiment, the electrolytic sulfuric acid apparatus 1, the electrolytic circuit, the pumps 12 and 14, the filters 13 and 17, the cooler 15 and the heater 16 constitute the electrolytic sulfuric acid solution manufacturing apparatus of the present invention.

Next, the operation of the cleaning system shown in FIG. 1 will be described.
In this cleaning system, a sulfuric acid solution having a relatively low sulfuric acid concentration is supplied from the primary concentrated sulfuric acid supply line 8A. At that time, the concentration may be adjusted by supplying pure water from the pure water supply line 7. When the concentration is not adjusted, the supplied sulfuric acid solution corresponds to the primary sulfuric acid solution. When the concentration is adjusted, the adjusted sulfuric acid solution corresponds to the primary sulfuric acid solution. Thus, the primary sulfuric acid solution is stored in the sulfuric acid solution storage tank 3. It is desirable to adjust the sulfuric acid solution for primary use so that the sulfuric acid concentration is in the range of 30% by mass to 50% by mass. Electrolysis can be performed efficiently within this sulfuric acid concentration range.

  The primary sulfuric acid solution stored in the sulfuric acid solution storage tank 3 is sent by the pump 5 to the electrolytic cell 2 through the feed circulation line 4A. At this time, the primary sulfuric acid solution is cooled to a temperature suitable for electrolysis by the cooler 6. In this cooling, for example, it is desirable to cool so that the electrolysis temperature is 10 to 90 ° C.

  In the electrolysis cell 2, the sulfuric acid in the primary sulfuric acid solution, which is energized at a desired current density between the anode 2A and the cathode 2B and passed between them, is electrolyzed, and persulfuric acid (peroxomonosulfuric acid, peroxodisulfuric acid) is used as the oxidizing substance. Sulfuric acid), ozone, and hydrogen peroxide are produced to form a primary electrolytic sulfuric acid solution. The primary electrolytic sulfuric acid solution is sent and stored in the sulfuric acid solution storage tank 3 through the return circulation line 4B. A gas / liquid separator (not shown) may be provided in the return circulation line 4B to remove gas components such as oxygen, hydrogen, and ozone in the primary electrolytic sulfuric acid solution.

The electrolysis time of the primary electrolytic sulfuric acid solution in the sulfuric acid solution storage tank 3 can be set by measurement with an appropriate measuring instrument, electrolysis time or the like. If the target persulfuric acid concentration is obtained or estimated to be obtained by continuing electrolysis, the electrolysis is temporarily stopped.
Next, in the sulfuric acid solution storage tank 3, a sulfuric acid solution having a relatively high sulfuric acid concentration is supplied from the secondary concentrated sulfuric acid supply line 8B. At that time, the concentration may be adjusted by supplying pure water from the pure water supply line 7. When the concentration is not adjusted, the supplied sulfuric acid solution corresponds to the secondary sulfuric acid solution. When the concentration is adjusted, the adjusted sulfuric acid solution corresponds to the secondary sulfuric acid solution.

As described above, the secondary sulfuric acid solution is charged into the primary electrolytic sulfuric acid solution, and the secondary electrolytic sulfuric acid solution is stored in the sulfuric acid solution storage tank 3. It is desirable to adjust the secondary electrolytic sulfuric acid solution so that the sulfuric acid concentration is in the range of 80% by mass to 92% by mass. A sulfuric acid concentration of 80% by mass to 92% by mass sufficiently exhibits the oxidizing power of sulfuric acid and provides a high cleaning ability. For this reason, as the sulfuric acid concentration of the secondary sulfuric acid solution, concentrated sulfuric acid, for example, a concentrated sulfuric acid of about 96% by mass can be used. However, the sulfuric acid concentration of the secondary sulfuric acid solution is not limited to this.
Further, when the secondary electrolytic sulfuric acid solution is generated, the persulfuric acid concentration in the primary electrolytic sulfuric acid solution may be set so that the persulfuric acid concentration becomes a desired concentration.

The secondary electrolytic sulfuric acid solution in the sulfuric acid solution storage tank 3 is fed by the pump 12 to the batch type washing tank 10 through the circulation line 11A, and is further fed to the return circulation line 11B, the branch path 11C and the entire system by the pump 14. The secondary electrolytic sulfuric acid solution is allowed to spread.
After the secondary electrolytic sulfuric acid solution is spread over the entire cleaning system (after squeezing), the electronic material 100 is immersed in the batch-type cleaning tank 10 and the electrolytic electrolytic sulfuric acid solution is electrolyzed on the electrolytic sulfuric acid apparatus 1 side. The secondary electrolytic sulfuric acid solution is circulated between the batch type washing tank 10 and the sulfuric acid solution storage tank 3 by the feed circulation line 11A and the return circulation line 11B. In addition, the electrolysis of the secondary electrolytic sulfuric acid solution can be performed under energizing conditions different from the energizing conditions when the primary electrolytic sulfuric acid solution is generated. For example, when the sulfuric acid concentration is higher than 50% by mass, the diamond electrode is liable to be worn out even at a low current. Therefore, the electrolytic solution temperature of the primary sulfuric acid solution (50% by mass or less) is 40 to 60 ° C., and the current density is 0. 1 to 1 A / m ² , secondary electrolytic sulfuric acid solution (80 mass% or more) electrolysis solution temperature 40 to 60 ° C., current density 0.01 to 0.5 A / m ² , primary sulfuric acid as required It is conceivable to prevent electrode wear by making the current density for the secondary electrolytic sulfuric acid solution smaller than the solution.
Electrolysis of the secondary electrolytic sulfuric acid solution should be performed immediately after mixing concentrated sulfuric acid with a high concentration to form the secondary electrolytic sulfuric acid solution, and before distributing the secondary electrolytic sulfuric acid solution to the system. May be.

When supplying the secondary electrolytic sulfuric acid solution, the filter 13 provided in the feed circulation line 11A captures fine particles contained in the secondary electrolytic sulfuric acid solution and removes them from the secondary electrolytic sulfuric acid solution.
On the other hand, the secondary electrolytic sulfuric acid solution already used for cleaning in the batch-type cleaning tank 10 is returned by the pump 14 through the circulation line 11B, and a part of the secondary electrolytic sulfuric acid solution is cooled by the cooler 15. The solution is sent to the sulfuric acid solution storage tank 3. The other secondary electrolytic sulfuric acid solution passes through the branch path 11C, is heated by the heater 16, and after the fine particles are captured by the filter 17, joins the secondary electrolytic sulfuric acid solution sent from the sulfuric acid solution storage tank 3. Then, it is fed to the batch type washing tank 10 as a washing liquid.

  The secondary electrolytic sulfuric acid solution fed to the batch-type cleaning tank 10 is instantaneously formed by the merging of the secondary electrolytic sulfuric acid solution that has passed through the branch path 11C and the secondary electrolytic sulfuric acid solution fed from the sulfuric acid solution storage tank 3. The temperature is raised to a temperature suitable for cleaning. Specifically, a suitable temperature is 100 to 150 ° C, and a range of 120 to 140 ° C is more preferable. When the temperature of the secondary electrolytic sulfuric acid solution as the cleaning liquid is low, decomposition by persulfuric acid does not proceed sufficiently in the batch method, and the cleaning effect such as resist peeling of the electronic material 100 is reduced. If the temperature of the cleaning solution is too high, persulfuric acid will self-decompose at an early stage, and similarly, a sufficient cleaning effect such as resist stripping cannot be obtained. Therefore, in the heater 16, the persulfuric acid-containing sulfuric acid solution is heated so that the solution temperature is obtained.

(Embodiment 2)
FIG. 2 shows a modification of the batch-type sulfuric acid recycle type cleaning system of the first embodiment, and has a common configuration except for the configuration relating to the supply of the primary sulfuric acid solution and the supply of the secondary sulfuric acid solution. About the structure which is common in Embodiment 1, the same code | symbol is attached | subjected, the description is used, and the description is abbreviate | omitted or simplified here.

  In this embodiment, a pure water supply line 7 and a secondary concentrated sulfuric acid supply line 8B are connected to the sulfuric acid solution storage tank 3, respectively. The pure water supply line 7 is provided with an open / close valve 70, and the secondary concentrated sulfuric acid supply line 8B is provided with an open / close valve 80. The secondary concentrated sulfuric acid supply line 8B corresponds to a secondary sulfuric acid solution supply unit, and the pure water supply line 7 corresponds to a pure water supply unit. In addition, the sulfuric acid solution having a predetermined sulfuric acid concentration can be stored in the sulfuric acid solution storage tank 3 by adjusting the opening and closing of the open / close valves 70 and 80. Therefore, the secondary concentrated sulfuric acid supply line 8B and the pure water supply line 7 constitute a primary sulfuric acid solution supply unit.

Further, the control unit 30 is connected to the open / close valves 70 and 80 in a controllable manner. The control unit 30 can be configured by a CPU, a program that operates the CPU, a storage unit, and the like. By the operation of the control unit 30, the sulfuric acid solution having a predetermined sulfuric acid concentration can be stored in the sulfuric acid solution storage tank 3 by controlling the opening and closing of the open / close valves 70 and 80. The sulfuric acid concentration can be adjusted based on an estimated flow rate obtained by measuring the opening time of the open / close valves 70 and 80 (correlation is obtained in advance), a measurement result in which a flow meter is provided in the line, or the like.
In addition, the controller 30 replenishes the solution from the pure water supply line 7 or the secondary concentrated sulfuric acid supply line 8B when the sulfuric acid concentration or the amount of the secondary electrolytic sulfuric acid solution is changed after the system is operated. Then, the sulfuric acid concentration and the solution amount may be adjusted.

  In the first and second embodiments, although not shown, a return circulation line and a branch path may not be provided, and the cleaning drainage may be configured to be a one-time configuration for discharging out of the system.

(Embodiment 3)
Next, a single-wafer sulfuric acid recycling type cleaning system in FIG. 3 will be described. In addition, about the structure similar to the said Embodiment 1, the same code | symbol is attached | subjected, the description is used, and the description is abbreviate | omitted or simplified here.
In the cleaning system of this embodiment, an electrolytic cell 2 that performs electrolysis while passing a sulfuric acid solution, and a sulfuric acid solution storage tank 3 that stores a sulfuric acid solution (including an electrolytic sulfuric acid solution after electrolysis) include a feed circulation line 4A. It is connected to the return circulation line 4B, and has an electrolytic sulfuric acid apparatus 1 similar to the electrolytic sulfuric acid apparatus 1 of the first embodiment.
Furthermore, in this embodiment, the gas-liquid separation tank 9 is interposed in the return circulation line 4B. In the gas-liquid separation tank 9, the gas in the sulfuric acid solution containing the gas is separated by electrolysis and discharged out of the system, and a known one can be used. In the present invention, gas-liquid separation is possible. If there is, the configuration is not particularly limited.

Further, the sulfuric acid solution storage tank 3 is connected by a single-wafer cleaning machine 20 on the use side, a feed circulation line 21A, and a return circulation line 21B. In this embodiment, the feed circulation line 21A corresponds to an electrolyte supply path.
In the feed circulation line 21 </ b> A, a pump 22, a filter 23, and a heater 24 are interposed in this order in the feed direction from the sulfuric acid solution storage tank 3 to the single wafer cleaning machine 20. The front end side in the feed direction of the feed circulation line 21 </ b> A is connected to the single wafer cleaning machine 20.
Note that a one-time heater can be suitably used for the heater 24. The solution in the sulfuric acid solution storage tank 3 is preferably adjusted to 50 to 90 ° C.

  In the single wafer cleaning machine 20, the secondary electrolytic sulfuric acid solution for cleaning supplied from the feed circulation line 21A is sprayed, dripped, or flows down onto the electronic material 100 installed in the single wafer cleaning machine 20. Etc. are provided. Note that a solution may be sprayed on the electronic material 100 by applying pressure when dropping or flowing.

In the single wafer cleaning machine 20, a return circulation line 21 </ b> B for discharging cleaning waste liquid and a drain line 21 </ b> C are connected, and the drain line 21 </ b> C is connected to a pure water drain tank 29. The drainage used for cleaning is sent to the pure water drainage tank 29 through the drainage line 21C by a valve operation or the like, and is mixed with pure water inside to reduce the sulfuric acid concentration and the like so that it can be discarded. In the return circulation line 21B, a sulfuric acid drainage tank 25 is interposed, and a pump 26, a filter 27, and a cooler 28 are arranged in this order in the feed direction from the single wafer cleaning machine 20 to the sulfuric acid solution storage tank 3. Has been.
In the case of unused drainage other than at the time of cleaning, the drainage from the single wafer cleaning machine 20 is connected to the return circulation line 21B and the sulfuric acid drainage tank 25 by valve operation or the like, and unused secondary electrolysis. The sulfuric acid solution is collected in the sulfuric acid drainage tank 25.

Next, the operation of the single wafer cleaning system will be described.
In the sulfuric acid solution storage tank 3, a sulfuric acid solution for primary use having a sulfuric acid concentration of 30% by mass to 50% by mass is accommodated in the same manner as described above, and the primary electrolytic sulfuric acid is circulated through the electrolytic cell 2 and electrolyzed. Create a solution.
A secondary sulfuric acid solution is mixed with the primary electrolytic sulfuric acid solution to obtain a secondary electrolytic sulfuric acid solution having a sulfuric acid concentration of 80% by mass to 92% by mass. Other conditions are the same as in the first embodiment.

The secondary electrolytic sulfuric acid solution in the sulfuric acid solution storage tank 3 may be electrolyzed while circulating the secondary electrolytic sulfuric acid solution between the electrolytic cell 2 until a desired persulfuric acid concentration is obtained. Immediately after mixing with the sulfuric acid solution for the next time, supply to the use side may be performed.
Moreover, you may start electrolysis so that the persulfuric acid concentration of a secondary electrolytic sulfuric acid solution may be maintained with supply. Electrolysis may be performed continuously or intermittently.

  In supplying the secondary electrolytic sulfuric acid solution from the sulfuric acid solution storage tank 3, the solution is fed by the pump 22 through the feed circulation line 21 </ b> A. The secondary electrolytic sulfuric acid solution flowing through the feed circulation line 21 </ b> A is captured and removed by the filter 23, and then introduced into the heater 24 and heated to, for example, 80 to 150 ° C.

The heated secondary electrolytic sulfuric acid solution is sent to the single wafer cleaning machine 20 and is brought into contact with the electronic material 100 by spraying, dripping, or flowing down, and unnecessary substances such as a resist on the electronic material 100 are removed.
The drainage used for the cleaning can be sent to the pure water drainage tank 29 through the drainage line 21C to be drained. Moreover, the secondary electrolytic sulfuric acid solution that is not used for cleaning, or the drained liquid that is considered to have a small amount of removed substances in the later stage of cleaning, can be collected in the sulfuric acid draining tank 25 through the return circulation line 21B. The solution in the sulfuric acid drainage tank 25 is sent back by the pump 26 toward the sulfuric acid solution storage tank 3 through the circulation line 21B. After the particles are captured and removed by the filter 27, the solution is cooled by the cooler 28 (for example, Cooled to 45 ° C. to 55 ° C.) and sent to the sulfuric acid solution storage tank 3. The sulfuric acid solution returned to the sulfuric acid solution storage tank 3 can be circulated between the electrolytic cell 2 to regenerate persulfuric acid.

(Embodiment 4)
FIG. 4 shows a modification of the single-wafer sulfuric acid recycling cleaning system of Embodiment 3, and has a common configuration except for the configuration relating to the supply of the primary sulfuric acid solution and the supply of the secondary sulfuric acid solution. . About the structure which is common in Embodiment 1-3, the same code | symbol is attached | subjected, the description is used, and the description is abbreviate | omitted or simplified here.

Also in this embodiment, the pure water supply line 7 and the secondary concentrated sulfuric acid supply line 8B are respectively connected to the sulfuric acid solution storage tank 3 as in the second embodiment. The pure water supply line 7 is provided with an open / close valve 70, and the secondary concentrated sulfuric acid supply line 8B is provided with an open / close valve 80. The secondary concentrated sulfuric acid supply line 8B and the pure water supply line 7 constitute a primary sulfuric acid solution supply unit.
Also in this embodiment, the control unit 30 is connected to the open / close valves 70 and 80 in a controllable manner.

  In the third and fourth embodiments, although not shown, a return circulation line is not provided, and the cleaning waste liquid may be a one-time configuration for discharging out of the system.

Next, the procedure in each of the above embodiments will be briefly described with reference to the flowchart of FIG.
First, the primary sulfuric acid solution is stored (step s1). In this case, the primary sulfuric acid solution is adjusted to have a sulfuric acid concentration of 30% by mass to 50% by mass. Next, the primary sulfuric acid solution is electrolyzed (step s2). Next, it is determined whether a predetermined persulfuric acid concentration has been reached (step s3). Whether a persulfuric acid concentration of a predetermined level or more is obtained may be determined by measuring the persulfuric acid concentration or by predicting the required time for electrolysis in advance. When it is determined that the predetermined persulfuric acid concentration has not been reached (No in step s3), the process returns to step s2 and electrolysis is continued.

When it is determined that the predetermined persulfuric acid concentration has been reached (step s3, Yes), the secondary sulfuric acid solution is generated by adding the secondary sulfuric acid solution to the obtained primary electrolytic sulfuric acid solution (step s4). At this time, the sulfuric acid concentration of the secondary electrolytic sulfuric acid solution is adjusted to 80% by mass to 92% by mass.
Next, the secondary electrolytic sulfuric acid solution is electrolyzed (step s5), and it is determined whether the electrolyzed secondary electrolytic sulfuric acid solution has reached a predetermined persulfuric acid concentration (step s6). If it is assumed that a desired persulfuric acid concentration has been reached when the secondary sulfuric acid solution is mixed with the primary electrolytic sulfuric acid solution, step s5 is omitted.

When it is determined in step s6 that the predetermined persulfuric acid concentration has not been reached (No in step s6), the process returns to step s5 to continue the electrolysis.
If it is determined in step s6 that the predetermined persulfuric acid concentration has been reached (step s6, Yes), the secondary electrolytic sulfuric acid solution is supplied or circulated to the user side (step s7).
Next, it is determined whether or not the process is completed. If not completed (No in step s8), the process returns to step s5 to continue electrolysis of the secondary electrolytic sulfuric acid solution. If it is finished (step s8, Yes), the procedure is finished.

Example 1
Using an electrolysis apparatus in which an electrode in which a conductive diamond thin film was deposited on a conductive silicon substrate was incorporated in the anode and the cathode, the oxidizing agent production efficiency when the sulfuric acid concentration was varied was measured. The electrolysis conditions were as follows: the electrolyte temperature was 50 ° C., the current density was 0.5 A / m ^2, and the oxidant concentration at 10 [Ah / L] was compared in terms of the input current amount per unit volume. The results are shown in FIG. The oxidant concentration was determined using an iodometric titration method.
As shown in FIG. 6, it can be seen that when the input current amount is 10 [Ah / L], the oxidant generation efficiency is high when the sulfuric acid concentration is 30 to 50 [mass%].

(Example 2)
In the batch type cleaning system using the electrolytic sulfuric acid solution shown in FIG. 1, the start-up time from the start of sulfuric acid filling to the start of wafer cleaning in the case of initial electrolysis with 40% by mass of sulfuric acid was measured. The sulfuric acid concentration at the start of wafer cleaning was 85 ± 1% by mass, and the oxidizing agent concentration was 25 mM or more. Note that the amount of liquid retained is about 100 L for the entire system including the cleaning tank side 55 L, the electrolytic sulfuric acid apparatus side 40 L, and the communication pipe 5 L. The connecting piping is a feed circulation line 4A, a return circulation line 4B, a feed circulation line 11A, a return circulation line 11B, and a branch path 11C.
The circulation flow rate on the washing tank side and the electrolytic sulfuric acid apparatus side was about 10 L / min, and 96 mass% sulfuric acid stock solution and ultrapure water for concentration adjustment were added at about 5 L / min on the electrolytic sulfuric acid apparatus side. In the electrolysis apparatus (electrolysis cell), the electrolysis conditions of the primary sulfuric acid solution and the secondary electrolytic sulfuric acid solution (s2 and s5 in FIG. 5) are both 840 A at an electrolysis temperature of 50 ° C. and a current density of 0.5 A / m ^2. The current was turned on. Table 1 shows the contents of the four steps, the state at the time of completion of each step, and the step time until the start-up is completed. In the case of this method, the start-up process is completed in about 60 minutes, and the wafer cleaning can be started.

(Example 3)
In the same apparatus and operating conditions as in Example 2, the sulfuric acid concentration at the start of wafer cleaning was 92 ± 1% by mass, and the oxidizing agent concentration was 35 mM or more. Table 2 shows the contents of the four processes, the state at the completion of each process, and the process time until the start-up is completed. In the case of this method, the start-up process is completed in about 70 minutes, and the wafer cleaning can be started.

(Comparative Example 1)
In the same apparatus and operating conditions as in Example 2, 85% by mass of sulfuric acid was applied to the entire apparatus while adjusting the concentration, and then electrolysis was performed to generate a predetermined oxidant concentration. The start-up time of was measured. The target values of the sulfuric acid concentration and the oxidant concentration at the start of wafer cleaning were the same as in Example 2. Table 3 shows the contents of the two processes, the state at the completion of each process, and the process time until the start-up is completed. In the case of this method, although the number of steps is small, the electrolysis time for raising the oxidant concentration to the target value becomes long, and the start-up step is completed in about 75 minutes and the wafer cleaning is started.

(Comparative Example 2)
In the same apparatus and operating conditions as in Example 3, 92% by mass of sulfuric acid was applied to the entire apparatus while adjusting the concentration, and then electrolysis was performed to generate a predetermined oxidant concentration. From the start of sulfuric acid application to the start of wafer cleaning. The start-up time of was measured. The target values of the sulfuric acid concentration and the oxidant concentration at the start of wafer cleaning were the same as in Example 2. Table 4 shows the contents of the two processes, the state at the completion of each process, and the process time until the start-up is completed. When the sulfuric acid concentration is increased, the generation efficiency of the oxidizing agent by electrolysis is greatly reduced. With this method and conditions, it takes about 170 minutes to complete the start-up process, and it can be seen that the start-up time is significantly longer than that in Example 3.

DESCRIPTION OF SYMBOLS 1 Electrolytic sulfuric acid apparatus 2 Electrolytic cell 3 Sulfuric acid solution storage tank 4A Feed circulation line 4B Return circulation line 7 Pure water supply line 8A Primary concentrated sulfuric acid supply line 8B Secondary concentrated sulfuric acid supply line 10 Batch type washing tank 11A Feed circulation line 11B Return circulation line 20 Single wafer cleaning machine 21A Feed circulation line 21B Return circulation line 30 Control unit 100 Electronic material

Claims (10)

Of the methods for producing an electrolytic sulfuric acid solution of the present invention, the first present invention comprises:
A method for producing an electrolytic sulfuric acid solution using a primary sulfuric acid solution and a secondary sulfuric acid solution having a relatively high sulfuric acid concentration relative to the primary sulfuric acid solution,
The primary sulfuric acid solution is electrolyzed to form a primary electrolytic sulfuric acid solution, and the secondary sulfuric acid solution is mixed with the primary electrolytic sulfuric acid solution to adjust the sulfuric acid concentration to a predetermined concentration. A method for producing an electrolytic sulfuric acid solution, wherein a sulfuric acid solution is generated and the electrolysis is performed while circulating the sulfuric acid solution between a sulfuric acid electrolysis cell and a sulfuric acid solution storage tank.   The sulfuric acid concentration of the primary electrolytic sulfuric acid solution is in the range of 30% by mass to 50% by mass, and the sulfuric acid concentration of the secondary electrolytic sulfuric acid solution is in the range of 80% by mass to 92% by mass. Item 2. A method for producing an electrolytic sulfuric acid solution according to Item 1.   3. The method for producing an electrolytic sulfuric acid solution according to claim 1, wherein at least an anode surface of the electrodes used for electrolysis is a conductive diamond. 4.   The electrolytic sulfuric acid solution production according to any one of claims 1 to 3, wherein the secondary electrolytic sulfuric acid solution is electrolyzed while circulating the secondary electrolytic sulfuric acid solution to and from the use side. Method.   The method for producing an electrolytic sulfuric acid solution according to any one of claims 1 to 4, wherein the use side is a cleaning process facility that removes an object to be removed from an electronic material.   The secondary sulfuric acid solution is mixed with the primary electrolytic sulfuric acid solution to form the secondary electrolytic sulfuric acid solution, and then the secondary electrolytic sulfuric acid solution is distributed between the user side and the user side. The method for producing an electrolytic sulfuric acid solution according to any one of claims 1 to 5, wherein the secondary electrolytic sulfuric acid solution is electrolyzed with the use of the secondary electrolytic sulfuric acid solution.   The secondary electrolytic sulfuric acid solution is mixed with the primary electrolytic sulfuric acid solution to form the secondary electrolytic sulfuric acid solution, and then the secondary electrolytic sulfuric acid solution is electrolyzed. 2. A method for producing an electrolytic sulfuric acid solution according to item 1.   The electrolysis of the secondary electrolytic sulfuric acid solution is performed by collecting and circulating the secondary electrolytic sulfuric acid solution sent to the use side and subjecting the secondary electrolytic sulfuric acid solution to the electrolysis. A method for producing an electrolytic sulfuric acid solution. A sulfuric acid electrolysis cell;
An electrolyte reservoir,
An electrolytic circulation path for circulating a solution between the sulfuric acid electrolysis cell and the electrolytic solution storage tank; and an electrolytic solution supply path for supplying a solution from the electrolytic solution storage tank to a use facility of electrolytic sulfuric acid, A primary sulfuric acid solution supply unit for supplying a sulfuric acid solution to the electrolytic solution storage tank, and a secondary sulfuric acid for supplying a sulfuric acid solution having a relatively high sulfuric acid concentration to the sulfuric acid solution supplied from the primary sulfuric acid solution supply unit A solution supply unit is connected, and the primary sulfuric acid solution supply unit and the secondary sulfuric acid solution supply unit can switch the solution supply to the electrolyte storage tank. Electrolytic sulfuric acid solution production equipment.   The primary sulfuric acid solution supply unit includes a secondary sulfuric acid solution supply unit and a pure water supply unit, and the secondary sulfuric acid solution and pure water are supplied and mixed in a pipe or in a storage tank to a predetermined concentration. The apparatus for producing an electrolytic sulfuric acid solution according to claim 9, wherein the electrolytic sulfuric acid solution manufacturing apparatus is configured to be adjusted to generate a primary sulfuric acid solution.

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