Device for recovering sulfuric acid and method for recovering sulfuric acid

Abstract

To provide a device and a method for recovering sulfuric acid capable of efficiently reducing the concentration of hydrogen peroxide in the recovered sulfuric acid and discharging it.SOLUTION: A sulfuric acid recovery device 100 includes a primary recovery tank 102, a concentration meter, a discharge pipe 120, a circulation pipe 122, a valve 132, a pump 110, and a control circuit. The primary recovery tank recovers sulfuric acid that includes hydrogen peroxide. The concentration meter measures the concentration of the hydrogen peroxide. The discharge pipe discharges sulfuric acid from the primary recovery tank to a second recovery tank 302. The maximum height position of the circulation pipe is set below the maximum height position of the discharge pipe, and a flow path is formed so as to return sulfuric acid discharged from the primary recovery tank to the primary recovery tank. The valve opens and closes the flow path of the discharge pipe. The pump sends sulfuric acid discharged from the primary recovery tank to at least the circulation pipe out of the circulation pipe and the discharge pipe. The control circuit controls the opening and closing of the valve according to the concentration of hydrogen peroxide measured by the concentration meter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a sulfuric acid recovery apparatus and a sulfuric acid recovery method. [Background technology]

[0002] In the process of semiconductor manufacturing, in the process using sulfuric acid, used sulfuric acid is discharged from the process chamber. Therefore, it becomes necessary to recover the used sulfuric acid. The used sulfuric acid is collected in a recovery tank and then transported away. In the process using sulfuric acid, hydrogen peroxide may be used in addition to sulfuric acid. In such a process, the sulfuric acid recovered from the process chamber contains hydrogen peroxide.

[0003] Here, for example, in order to transport sulfuric acid by a tank truck or the like, it is required that the hydrogen peroxide contained in the sulfuric acid is less than a predetermined concentration. On the other hand, as the generation of semiconductor devices manufactured changes, the amount of sulfuric acid and hydrogen peroxide used in the process increases. Therefore, the concentration of hydrogen peroxide in the recovered sulfuric acid also tends to increase. Therefore, in order to transport the recovered sulfuric acid, it is desired to efficiently reduce the concentration of hydrogen peroxide in the recovered sulfuric acid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2019 / 0067048 Summary of the Invention [Problem to be solved by the invention]

[0005] An embodiment of the present invention provides an apparatus and method for recovering sulfuric acid that can efficiently reduce the concentration of hydrogen peroxide in the recovered sulfuric acid and then discharge the hydrogen peroxide. [Means for solving the problem]

[0006] The sulfuric acid recovery device of the embodiment includes a first recovery tank, a concentration meter, a discharge pipe, a circulation pipe, a first valve, a pump, and a control circuit. The first recovery tank recovers sulfuric acid containing hydrogen peroxide. The concentration meter measures the concentration of the hydrogen peroxide contained in the sulfuric acid in the first recovery tank. The discharge pipe discharges the sulfuric acid from the first recovery tank to a second recovery tank. The circulation pipe has a maximum height position set below a maximum height position of the discharge pipe, and a flow path is formed so as to return the sulfuric acid discharged from the first recovery tank to the first recovery tank. The first valve opens and closes the flow path of the discharge pipe. The pump sends the sulfuric acid discharged from the first recovery tank to at least the circulation pipe out of the circulation pipe and the discharge pipe. The control circuit controls the opening and closing of the first valve according to the concentration of the hydrogen peroxide measured by the concentration meter. [Brief description of the drawings]

[0007] [Figure 1] 1 is a diagram showing an example of the configuration of a sulfuric acid recovery device in a first embodiment. [Diagram 2] FIG. 4 is a diagram showing an example of a sulfuric acid recovery apparatus in a comparative example of the first embodiment. [Diagram 3] FIG. 2 is a diagram for explaining a method for reducing the concentration of hydrogen peroxide in sulfuric acid in the first embodiment. [Figure 4] FIG. 4 is a diagram showing an example of pipe diameters of a discharge pipe and a circulation pipe in the first embodiment. [Diagram 5] FIG. 4 is a diagram for explaining a method for discharging sulfuric acid in the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] (First embodiment) Fig. 1 is a diagram showing an example of the configuration of a sulfuric acid recovery apparatus in the first embodiment. In Fig. 1, the sulfuric acid recovery apparatus 100 includes a primary recovery tank 102 (first recovery tank), a pump 110, a concentration meter 112, a discharge pipe 120, a circulation pipe 122, valves 130, 132, 134, and a control circuit 140.

[0009] The sulfuric acid recovery apparatus 100 is disposed, for example, in a clean room CR.

[0010] In the same or different clean room CR as the sulfuric acid recovery apparatus 100, for example, a plurality of process chambers 200, 202 are arranged. In the example of FIG. 1, the process chamber 200 uses sulfuric acid (H2SO4) alone for the process, and discharges used sulfuric acid through a pipe. In the process chamber 202, sulfuric acid containing hydrogen peroxide (H2O2) is used for the process, and discharges used sulfuric acid containing hydrogen peroxide through a pipe. The sulfuric acid recovery apparatus 100 recovers sulfuric acid discharged from these plurality of process chambers 200, 202. In this way, the sulfuric acid recovery apparatus 100 may recover both sulfuric acid containing hydrogen peroxide and sulfuric acid not containing hydrogen peroxide. The sulfuric acid recovery apparatus 100 may recover only sulfuric acid containing hydrogen peroxide.

[0011] The primary recovery tank 102 is formed of a material that is resistant to chemicals such as sulfuric acid. For example, a PTFE (polytetrafluoroethylene) lined tank or the like is used. The primary recovery tank 102 is formed with an exhaust port 104, an exhaust port 106, a suction port 108, and a suction port 109. The exhaust port 104 is disposed on the bottom surface of the primary recovery tank 102. The exhaust port 106, the suction port 108, and the suction port 109 are disposed on the upper surface of the primary recovery tank 102. 1 shows a case where the discharge port 104 is disposed on the bottom surface of the primary recovery tank 102, but this is not limited thereto. The discharge port 104 may also be disposed on the lower part of the side surface of the primary recovery tank 102.

[0012] The sulfuric acid discharged from the multiple process chambers 200, 202 is collected in the primary recovery tank 102 through a suction port 108 located in the upper part of the primary recovery tank 102. Therefore, the primary recovery tank 102 collects the discharged sulfuric acid containing hydrogen peroxide. Therefore, the sulfuric acid containing hydrogen peroxide is stored in the primary recovery tank 102.

[0013] The exhaust port 106 is connected to an external exhaust duct line. Hydrogen peroxide is a substance that is less stable than sulfuric acid and is easily decomposed into water and oxygen (O2). The decomposed oxygen gas is released from the sulfuric acid and is exhausted to the external exhaust duct line through the exhaust port 106.

[0014] An inlet of a pump 110 is connected to an outlet 104 disposed at the bottom of the primary recovery tank 102 via a valve 130. The outlet of the pump 110 is connected to a discharge pipe 120.

[0015] The discharge pipe 120 is made of a material resistant to chemicals such as sulfuric acid. For example, a PTFE-lined pipe or a PFA (perfluoroalkoxyalkane) tube is used. For protection, the discharge pipe 120 may be preferably configured to use a polyvinyl chloride pipe as an outer pipe and pass a pipe (tube) made of a material resistant to the above-mentioned chemicals inside the outer pipe. The discharge pipe 120 discharges sulfuric acid discharged from the primary recovery tank 102 to a secondary recovery tank 302 (second recovery tank). The secondary recovery tank 302 is disposed, for example, in a chemical supply room outside the clean room CR in which the sulfuric acid recovery device 100 is disposed. At this time, the discharge pipe 120 is once extended upward, then bent, for example, horizontally, and then connected from above to the secondary recovery tank 302 in the chemical supply room. The flow path of the discharge pipe 120 branches off midway as the discharge pipe 120 extends upward, and one end of the circulation pipe 122 is connected to the branched point via a valve 134 . Further, a valve 132 (first valve) is disposed near the branch point downstream of the branched discharge pipe 120. The valve 132 opens and closes the flow path of the discharge pipe 120. Specifically, the valve 132 opens and closes the flow path downstream of the discharge pipe 120 after branching into the circulation pipe 122. In the example of Fig. 1, an upstream portion 120a of the discharge pipe 120 from the pump 110 to the branch point and a downstream portion 120b of the discharge pipe 120 from the branch point are shown separately.

[0016] The circulation pipe 122 is made of a material resistant to chemicals such as sulfuric acid. For example, a PTFE-lined pipe or a PFA tube is used. In addition, the circulation pipe 122 may be preferably configured to use a polyvinyl chloride pipe as an outer pipe for protection, and a pipe (tube) made of a material resistant to the above-mentioned chemicals is passed inside the outer pipe. The circulation pipe 122 is formed with a flow path so that the sulfuric acid discharged from the first recovery tank 102 is returned to the first recovery tank 102. In the example of FIG. 1, the circulation pipe 122 extends upward from a branch position from the discharge pipe 120, and is then bent horizontally, for example, and connected to the first recovery tank 102 from above. Specifically, the other end of the circulation pipe 122 is connected to a suction port 109 disposed at the top of the first recovery tank 102. The upstream portion 120a of the discharge pipe 120 and the circulation pipe 122 form a circulation line that returns the sulfuric acid discharged from the first recovery tank 102 to the first recovery tank 102. The valve 134 (second valve) opens and closes the flow path of the circulation pipe 122. Alternatively, the valve 134 adjusts the opening degree of the flow path of the circulation pipe 122.

[0017] 1, the upstream portion 120a of the discharge pipe 120 is used in common for the discharge pipe 120 line and the circulation line up to the vicinity of the mid-height position of the discharge pipe 120, but this is not limited thereto. It is also preferable that the upstream portion 120a of the discharge pipe 120 is not used in common, but is branched at the discharge port of the pump 110, and the discharge pipe 120 and the circulation pipe 122 are provided separately.

[0018] A centrifugal pump such as a magnet pump is used as the pump 110. For example, an impeller-type chemical pump that is resistant to sulfuric acid is used as the pump 110. The pump 110 sends the sulfuric acid containing hydrogen peroxide discharged from the primary recovery tank 102 to at least one of the circulation pipe 122 and the discharge pipe 120.

[0019] In the case where the upstream portion 120a of the discharge pipe 120 is not shared but is branched near the pump 110 to provide the discharge pipe 120 and the circulation pipe 122 separately, the pump 110 may also be divided into a pump for the discharge pipe 120 and a pump for the circulation pipe 122. In the case where the pump is divided into a pump for the discharge pipe 120 and a pump for the circulation pipe 122, the pump for the circulation pipe 122 sends sulfuric acid containing hydrogen peroxide discharged from the primary recovery tank 102 to at least the circulation pipe 122 out of the circulation pipe 122 and the discharge pipe 120. The pump for the discharge pipe 120 sends sulfuric acid containing hydrogen peroxide discharged from the primary recovery tank 102 to at least the discharge pipe 120 out of the circulation pipe 122 and the discharge pipe 120.

[0020] The output of the concentration meter 112 is connected to a control circuit 140. Furthermore, the ON / OFF operation of the pump 110 and the opening and closing operations of the valves 130, 132, and 134 are controlled, for example, by the control circuit 140. In the example of Fig. 1, the wiring between the concentration meter 112, the pump 110, and the valves 130, 132, and 134 and the control circuit 140 is shown by dotted lines. However, this is not limited to this. The ON / OFF operation of the pump 110 and the opening and closing operations of the valves 130, 132, and 134 may be performed manually.

[0021] The sulfuric acid supplied to the pump 110 is sent by the pump 110 into the discharge pipe 120 and is recovered in a secondary recovery tank 302 connected to the discharge port of the discharge pipe 120. Specifically, the discharge port of the discharge pipe 120 is connected to a suction port 308 of the secondary recovery tank 302. The sulfuric acid recovered in the secondary recovery tank 302 is loaded onto a tank truck through a valve 330 from a discharge port 304 at the bottom of the secondary recovery tank 302, and is then disposed of or sold for a valuable purpose. A pump that sends sulfuric acid to the tank truck is connected to the downstream side of the valve 330, but this pump is not shown in the figure.

[0022] FIG. 2 is a diagram showing an example of a sulfuric acid recovery apparatus in a comparative example of the first embodiment. In the example of FIG. 2, the piping and suction port through which sulfuric acid containing hydrogen peroxide discharged from the process chamber enters the primary recovery tank 101 are omitted. In the example of FIG. 2, the horizontal direction is indicated as the x and y directions, and the height direction is indicated as the z direction. In the comparative example, a configuration in which a circulation line is not arranged is shown. Sulfuric acid containing hydrogen peroxide is stored in the primary recovery tank 101. Then, the sulfuric acid recovered in the primary recovery tank 101 is sent by a pump 111 through a discharge piping 121 to an external secondary recovery tank (not shown).

[0023] As described above, the amounts of sulfuric acid and hydrogen peroxide used in the process are increasing with the change in the generation of semiconductor devices manufactured. Therefore, the concentration of hydrogen peroxide in the sulfuric acid recovered in the primary recovery tank 101 also tends to increase. Therefore, it takes time for the concentration of hydrogen peroxide in the primary recovery tank 101 to naturally decrease. In addition, in such a state, the concentration of hydrogen peroxide remains high even if the sulfuric acid is sent to the secondary recovery tank, so not only is it impossible to sell the sulfuric acid at a value, but it is also difficult to transport it by tank truck. Therefore, it is desirable to efficiently decrease the concentration of hydrogen peroxide.

[0024] On the other hand, hydrogen peroxide is a more unstable substance than sulfuric acid, so if the pump 111 is operated in such a state, cavitation occurs. Specifically, the rotation of the rotor (impeller) of the centrifugal pump relatively reduces the pressure on the suction side of the pump 111, causing the hydrogen peroxide in the sulfuric acid to decompose and oxygen to appear as bubbles. In the first embodiment, this phenomenon is utilized to efficiently reduce the concentration of hydrogen peroxide in the sulfuric acid.

[0025] FIG. 3 is a diagram for explaining a method for reducing the concentration of hydrogen peroxide in sulfuric acid in the first embodiment. In the example of FIG. 3, the piping and the suction port through which sulfuric acid containing hydrogen peroxide discharged from the process chamber enters the first recovery tank 102 are omitted. In addition, in the example of FIG. 3, the configuration inside the chemical liquid supply chamber and the control circuit 140 are omitted. In the example of FIG. 3, the horizontal direction is indicated as the x and y directions, and the height direction is indicated as the z direction. In the first embodiment, the concentration meter 112 measures (monitors) the concentration of hydrogen peroxide in the sulfuric acid accumulated in the first recovery tank 102. The measurement may be performed continuously or at a predetermined sampling interval. For example, it is preferable to perform the measurement every few seconds or minutes.

[0026] In the first embodiment, if the concentration of hydrogen peroxide in the secondary recovery tank 302 is not less than, for example, 5 wt%, the tank truck cannot load the sulfuric acid, and therefore the sulfuric acid cannot be transported. Furthermore, if the concentration of hydrogen peroxide in the secondary recovery tank 302 is not less than, for example, 1 wt%, the recovered sulfuric acid cannot be sold for sale. Therefore, when the concentration of hydrogen peroxide measured by the concentration meter 112 is greater than a preset value, the control circuit 140 operates the pump 110 with the valve 132 closed and the valves 130 and 134 open. Then, the sulfuric acid containing hydrogen peroxide recovered in the primary recovery tank 102 is circulated between the circulation pipe 122 and the primary recovery tank 102. This generates cavitation, promotes the decomposition of hydrogen peroxide, and generates more oxygen bubbles.

[0027] In the first embodiment, as shown in FIG. 3, the discharge pipe 120 is routed from the height position of the floor of the clean room CR through a position where the maximum installation height position is height h1 to the secondary recovery tank 302 in the chemical liquid supply chamber shown in FIG. 1. The discharge pipe 120 branches at a height position lower than the height h1, and one end of the circulation pipe 122 is connected to the branched point via a valve 134. The circulation pipe 122 forms a maximum installation height position below the maximum installation height position of the discharge pipe 120. More preferably, the maximum installation height position of the circulation pipe 122 is set to a height h2 lower than the height h1, which is the maximum installation height position of the discharge pipe 120, as shown in FIG. 3. In the example of FIG. 3, the maximum installation height position is defined, for example, by the height position of the bottom of the pipe extending horizontally at the top.

[0028] FIG. 4 is a diagram showing an example of the pipe diameters of the discharge pipe and the circulation pipe in the first embodiment. The pipe diameter of the circulation pipe 122 is formed to be equal to or larger than the pipe diameter of the discharge pipe 120. The standard of the pipe size is generally defined according to the outer diameter size, but when the outer size is large, the inner diameter size is generally large. Here, it is sufficient that the inner diameter size of the circulation pipe 122 is equal to or larger than the inner diameter size of the discharge pipe 120. This makes it possible to make the pipe resistance of the circulation pipe 122 equal to or smaller than the pipe resistance of the discharge pipe 120. More preferably, as shown in FIG. 4, the pipe diameter of the circulation pipe 122 is formed to be larger than the pipe diameter of the discharge pipe 120. This makes it possible to make the pipe resistance of the circulation pipe 122 smaller than the pipe resistance of the discharge pipe 120.

[0029] Therefore, if the pump 110 has the head performance to push the sulfuric acid up to height h1, which is the maximum installation height of the discharge pipe 120, when cavitation occurs, the sulfuric acid can be circulated through the circulation pipe 122, whose maximum installation height is height h2, which is less than height h1, when cavitation occurs.

[0030] The circulated sulfuric acid contains oxygen gas bubbles generated by cavitation, which are released from the sulfuric acid when it returns to the primary recovery tank 102 and exhausted to an external exhaust duct line through the exhaust port 106. By repeatedly circulating the sulfuric acid, the concentration of hydrogen peroxide contained therein can be efficiently reduced.

[0031] Fig. 5 is a diagram for explaining a method of discharging sulfuric acid in the first embodiment. In the example of Fig. 5, the suction port through which the sulfuric acid containing hydrogen peroxide discharged from the process chamber enters the primary recovery tank 102 and the control circuit 140 are omitted. In addition, in the example of Fig. 5, the configuration inside the chemical liquid supply chamber is omitted. In the example of Fig. 5, the horizontal direction is indicated as the x and y directions, and the height direction is indicated as the z direction.

[0032] Control circuit 140 controls the opening and closing of valve 132 in response to the concentration of hydrogen peroxide measured by concentration meter 112. Similarly, control circuit 140 controls the opening and closing or the degree of opening of valve 134 in response to the concentration of hydrogen peroxide measured by concentration meter 112. Specifically, it operates as follows.

[0033] When the concentration of hydrogen peroxide measured by the concentration meter 122 falls below a predetermined value, the sulfuric acid circulating between the circulation pipe 122 and the primary recovery tank 102 is discharged to the secondary recovery tank 302 via the discharge pipe 120b. To this end, the control circuit 140 controls the valve 132 to change from a closed state to an open state when the concentration of hydrogen peroxide measured by the concentration meter 112 falls below the predetermined value from a state greater than the predetermined value. Similarly, the control circuit 140 controls the valve 134 to change from open to closed, or to reduce the degree of opening, when the concentration of hydrogen peroxide measured by the concentration meter 112 falls below the predetermined value. It is also possible to prevent shut-off operation of the pump 110 from occurring by not completely closing the valve 134.

[0034] As a result, sulfuric acid whose hydrogen peroxide concentration has fallen to a predetermined value or lower can be discharged via discharge pipe 120b to secondary recovery tank 302. In the state of the example of Fig. 5, since the hydrogen peroxide concentration is low, the amount of bubbles can be reduced even if cavitation occurs in pump 110. Therefore, the performance degradation of pump 110 can be suppressed or reduced, and sulfuric acid can be efficiently discharged.

[0035] When the discharged sulfuric acid is to be sold, the predetermined value of the hydrogen peroxide concentration here can be set to, for example, a value of 1 wt% or less. However, if oxygen gas bubbles are further generated due to cavitation while moving through the discharge pipe 120, the bubbles may escape from the sulfuric acid in the secondary recovery tank 302 as well. In view of this, the predetermined value may be set to a value of 1 wt% + α. It is preferable to set α to less than 1 wt%, for example, about 0.1 to 0.5 wt%.

[0036] On the other hand, if the sulfuric acid cannot be sold but can be transported by tanker truck, it is desirable to set the hydrogen peroxide concentration to a predetermined value of 5 wt % or less. Therefore, at least when the concentration of hydrogen peroxide measured by the concentration meter 112 is 5 wt % or less, the valve 132 is opened.

[0037] As a result of the above, the sulfuric acid recovered in the secondary recovery tank 302 has a hydrogen peroxide concentration of at least less than 5 wt%, so it is loaded onto a tank truck and transported. Furthermore, if the hydrogen peroxide concentration is less than 1 wt%, the transported sulfuric acid can be sold.

[0038] As described above, according to the first embodiment, the concentration of hydrogen peroxide in the recovered sulfuric acid can be efficiently reduced and then discharged.

[0039] Although the embodiments have been described above with reference to specific examples, the present invention is not limited to these specific examples.

[0040] In addition, all sulfuric acid recovery apparatuses and sulfuric acid recovery methods that include the elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention. [Explanation of symbols]

[0041] 100 sulfuric acid recovery device, 102 primary recovery tank, 110 pump, 112 concentration meter, 120 discharge pipe, 122 circulation pipe, 130, 132, 134 valve, 140 control circuit

Claims

1. a first recovery tank for recovering sulfuric acid containing hydrogen peroxide; a concentration meter for measuring a concentration of the hydrogen peroxide contained in the sulfuric acid in the first recovery tank; a discharge pipe for discharging the sulfuric acid from the first recovery tank to a second recovery tank; A circulation pipe having a maximum installation height position set to be equal to or lower than a maximum installation height position of the discharge pipe and a flow path formed to return the sulfuric acid discharged from the first recovery tank to the first recovery tank; A first valve that opens and closes a flow path of the exhaust pipe; a pump that sends the sulfuric acid discharged from the first recovery tank to at least the circulation pipe out of the circulation pipe and the discharge pipe; a control circuit that controls opening and closing of the first valve in response to the concentration of the hydrogen peroxide measured by the concentration meter; A sulfuric acid recovery apparatus comprising:

2. 2. The sulfuric acid recovery system according to claim 1, wherein the diameter of the circulation pipe is equal to or larger than the diameter of the discharge pipe.

3. 3. The sulfuric acid recovery system according to claim 1, wherein the pump is a centrifugal pump.

4. 3. The sulfuric acid recovery apparatus according to claim 1, wherein the control circuit controls the first valve to change from a closed state to an open state when the concentration of the hydrogen peroxide measured by the concentration meter falls from a state greater than a predetermined value to a state equal to or less than the predetermined value.

5. recovering sulfuric acid from both a first process chamber using sulfuric acid and a second process chamber using sulfuric acid and hydrogen peroxide in a first recovery tank; measuring the concentration of hydrogen peroxide contained in the sulfuric acid recovered in the first recovery tank; circulating the sulfuric acid recovered in the first recovery tank between a circulation pipe and the first recovery tank; When the measured concentration of hydrogen peroxide becomes equal to or lower than a predetermined value, the sulfuric acid circulating between the circulation pipe and the first recovery tank is discharged into a second recovery tank via a discharge pipe; A sulfuric acid recovery method comprising:

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