JP4862981B2 - Sulfuric acid recycle cleaning system and operation method thereof - Google Patents

Description

  The present invention relates to a sulfuric acid recycle type cleaning system that regenerates a persulfuric acid solution and uses it for cleaning while repeatedly using a sulfuric acid solution when cleaning and peeling a contaminant attached to a silicon wafer or the like with a persulfuric acid solution having a high peeling effect. And its operating method.

Wafer cleaning technology in the VLSI manufacturing process is a process for stripping and cleaning resist residues, fine particles, metals and natural oxide films, and ozone gas is blown into concentrated sulfuric acid and hydrogen peroxide mixed solution (SPM) or concentrated sulfuric acid. A solution (SOM) is frequently used. When hydrogen peroxide or ozone is added to high-concentration sulfuric acid, the sulfuric acid is oxidized to produce persulfuric acid. It is known that persulfuric acid has a high cleaning ability because it generates a strong oxidizing power when self-decomposing, and is useful for cleaning the wafer and the like.
As a method for producing persulfuric acid, in addition to the above method, there is also known a method in which an aqueous solution containing sulfate ions is electrolyzed in an electrolytic bath to obtain persulfuric acid-dissolved water and used for washing (Patent Documents 1 and 2). reference).

JP 2001-192874 A Special table 2003-511555 gazette

  By the way, in SPM, it is necessary to repeat the replenishment of the hydrogen peroxide solution in order to compensate for the self-decomposition when the persulfuric acid generated by the hydrogen peroxide solution self-decomposes and the oxidizing power decreases. When the sulfuric acid concentration falls below a certain concentration, it is exchanged with a new high concentration sulfuric acid. However, in the above method, since the persulfuric acid solution is diluted with water in hydrogen peroxide water, it is difficult to maintain a constant liquid composition. Further, the liquid is discarded and renewed every predetermined time or every processing batch. It is necessary to. For this reason, there are problems that the cleaning effect is not constant and a large amount of chemicals must be stored. On the other hand, in the SOM, the liquid is not diluted, and although the liquid renewal cycle can be generally longer than that of the SPM, the cleaning effect is inferior to that of the SPM.

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

  The present invention has been made against the background of the above circumstances, and by reusing persulfate ions from an aqueous solution of sulfuric acid by electrochemical action while repeatedly using sulfuric acid, the persulfate ions are recycled to greatly increase the amount of sulfuric acid used. It is an object of the present invention to provide a sulfuric acid recycle type cleaning system and an operation method thereof that can reduce the consumption of an electrode used in an electrochemical reaction as much as possible.

The invention of the operation method of the sulfuric acid recycling type cleaning system according to claim 1 comprises an electrolytic reaction device for regenerating a persulfate solution by generating persulfate ions from sulfate ions contained in the solution by an electrolytic reaction, and a persulfate solution. A plurality of cleaning devices for cleaning a material to be cleaned as a cleaning liquid, a plurality of circulation lines that individually connect the electrolytic reaction device and the plurality of cleaning devices to allow the persulfuric acid solution to circulate; An operation method of a sulfuric acid recycling type cleaning system comprising heating means for heating the cleaning liquid on the cleaning device side and cooling means for cooling the solution sent to the electrolytic reaction device, wherein the cleaning material is cleaned. In the cleaning apparatus, the circulation of the persulfuric acid solution with the electrolytic reaction apparatus is stopped, and at least one of the cleaning apparatuses that is not cleaning the material to be cleaned, The persulfuric acid solution is circulated by a circulation line with the electrolytic reaction apparatus in which the persulfuric acid solution is regenerated by the heating, and the heating on the washing device side in which the persulfuric acid solution is circulated during the regeneration. The cleaning liquid is maintained at a high temperature by means, and the temperature of the solution sent from the cleaning device side to the electrolytic reaction device is lowered by the cooling means.

The invention of the operation method of the sulfuric acid recycling type cleaning system according to claim 2 is the invention according to claim 1 , wherein in the circulation line, a relatively low temperature persulfuric acid solution feed from the electrolytic reaction device, Heat exchange is performed with a return liquid of a relatively high temperature persulfuric acid solution from the cleaning device.

The invention of claim 3 the method of operating a sulfuric acid recycle type cleaning system as claimed in the invention according to claim 1 or 2, persulfate between said electrolytic reaction apparatus and the cleaning device having been subjected to the cleaning of the cleaning material The step of regenerating the persulfuric acid solution until the persulfuric acid concentration reaches a predetermined concentration while circulating the working solution, and then the persulfuric acid solution is not circulated between the electrolytic reactor and the cleaning device. The step of cleaning the cleaning material is repeated.

The invention of the operation method of the sulfuric acid recycling type cleaning system according to claim 4 is the invention according to any one of claims 1 to 3 , wherein at least the anode of the electrodes provided in the electrolytic reaction apparatus is a conductive diamond electrode. It is characterized by.

The invention of the operation method of the sulfuric acid recycling type cleaning system according to claim 5 is the invention according to any one of claims 1 to 4 , wherein the conductive diamond electrode provided in the electrolytic reaction device is laminated on the substrate. It is a self-supporting conductive diamond electrode from which is removed.

The invention of the operation method of the sulfuric acid recycling type cleaning system according to claim 6 is the invention according to any one of claims 1 to 5 , wherein the regeneration is carried out in such a manner that the concentration of persulfuric acid during electrolysis in the electrolytic reaction apparatus is In order to satisfy the condition of persulfuric acid concentration [g / l] / TOC concentration [g / l] = 10 to 1000 with respect to the organic carbon concentration (TOC) generated by washing in the washing device circulated with the reactor. It is characterized by being performed until.

The invention of the sulfuric acid recycling type cleaning system according to claim 7 comprises an electrolytic reaction device for regenerating a persulfate solution by generating persulfate ions from sulfate ions contained in the solution by an electrolytic reaction, and a persulfate solution as a cleaning solution. A plurality of cleaning devices for cleaning the cleaning material, a plurality of circulation lines that individually connect the electrolytic reaction device and the plurality of cleaning devices to allow the persulfuric acid solution to circulate, and a connection to the electrolytic reaction device Selection switching means for selectively switching between the circulation line and the cleaning apparatus, a heating means for heating the cleaning liquid on each cleaning apparatus side, and a cooling means for cooling the solution sent from the cleaning apparatus to the electrolytic reaction apparatus, The heating means enables heating of the cleaning liquid on the side of the cleaning device connected by the selection switching means, and the cooling means is connected by the selection switching means and the solution Characterized in that it allows the cooling of the solution to be fed to the electrolytic reaction apparatus that performs electrolytic.

  According to the method of the present invention, persulfate ions in the cleaning liquid self-decompose to generate an oxidizing power, and contaminants (mainly organic substances) of the material to be cleaned are effectively peeled and cleaned by this oxidizing power. In the cleaning solution, the concentration of persulfuric acid gradually decreases due to self-decomposition of persulfate ions in the solution, but until the cleaning is completed, the persulfate solution containing contaminants is circulated between the electrolytic reactor and the electrolytic reactor. Is not done. Therefore, the contaminants are oxidatively decomposed by the persulfuric acid solution on the cleaning device side even after moving to the solution side. Here, when the persulfuric acid solution of the cleaning device is circulated with the electrolytic reaction device during the cleaning by the cleaning device, the contaminants separated from the device to be cleaned in the cleaning device flow into the electrolytic reaction device. The contaminants are directly oxidized by the electrodes provided in the electrolytic reaction device, thereby consuming the electrodes. However, in the present invention, as described above, the persulfuric acid solution being cleaned by the apparatus to be cleaned is not sent to the electrolytic reaction apparatus, so that the above-described consumption of the electrodes is avoided.

  Moreover, the solution in which the concentration of persulfuric acid is reduced by the self-decomposition of persulfate ions in the cleaning device is sent to the electrolytic reaction device through the circulation line after the cleaning is completed. In an electrolytic reaction apparatus, an anode and a cathode are immersed in a solution containing sulfate ions, and current is passed between the electrodes to perform electrolysis. As a result, sulfate ions in the solution are oxidized to produce persulfate ions, and a persulfate solution having a sufficiently high persulfate concentration is regenerated. The solution with increased persulfuric acid concentration is sent to the cleaning device through the circulation line. Then, by circulating the solution between the cleaning device and the electrolytic reaction device and repeating the above operation, the concentration of persulfuric acid in the solution can be further increased. In the electrolytic reaction, a target value of persulfuric acid concentration is determined in advance, and the regeneration can be terminated when the target value is reached. The persulfuric acid concentration can be known by measuring the concentration itself. In addition to this, the persulfuric acid concentration at the end of cleaning, the relationship between the electrolysis conditions (electrolysis current, electrolysis time) and the amount of persulfate ions generated in the electrolytic reaction apparatus are acquired in advance as data. The persulfate concentration may be estimated from these pieces of information in the process with reference to the data, and the electrolytic process may be stopped.

  Further, the target persulfuric acid concentration in the electrolytic reaction can be determined in consideration of the amount of contaminants of the cleaning material to be cleaned by the cleaning device. As this amount of contaminants, the total organic carbon concentration (TOC) produced | generated as a result of washing | cleaning in a washing | cleaning apparatus can be used. The target persulfuric acid concentration satisfies the condition of persulfuric acid concentration [g / l] / TOC concentration [g / l] = 10 to 1000 in order to oxidatively decompose the contaminants showing the TOC concentration. Is desirable. For the same reason, it is desirable to set the lower limit to 20 and the upper limit to 500. Therefore, it is desirable to produce a persulfuric acid-containing solution so that the ratio between the required amount of persulfuric acid and the TOC concentration satisfies the above conditions. For the TOC concentration, information on the TOC concentration in the material to be cleaned can be obtained in advance, and the persulfuric acid concentration target can be determined using the information in the same type of material to be cleaned.

In the present invention, a system is constructed by connecting a plurality of cleaning devices to one electrolytic reaction device through a circulation line, or a plurality of cleaning devices of a larger number are circulated to a plurality of electrolytic reaction devices. A system can be constructed by connecting with a line.
In the case where the cleaning device is connected to more than the number of electrolytic reaction devices (including one case), the cleaning device cleaning the material to be cleaned does not circulate the solution between the electrolytic reaction devices, While the solution is circulated between at least one cleaning device that has not cleaned the cleaning material and the electrolytic reaction device, electrolysis is performed in the electrolytic reaction device to regenerate the persulfuric acid solution, thereby increasing the persulfuric acid concentration.
During this oxidation treatment, the electrolytic reaction apparatus is connected to another washing tank, and the solution is circulated to produce a persulfuric acid-containing solution.
In a cleaning apparatus in which the persulfuric acid concentration is increased to a predetermined concentration, the persulfuric acid solution can be used as a cleaning liquid for cleaning the material to be cleaned. Since the oxidizing power of persulfate ions is strong, the oxidative decomposition treatment of contaminants can be performed only by retaining the solution only in the washing tank. On the other hand, in the cleaning apparatus that has completed the cleaning process, the solution is circulated between the electrolytic reaction apparatus and electrolysis is performed in the electrolytic reaction apparatus to regenerate the persulfuric acid solution in the same manner as described above. By repeating the above operation, wafer cleaning can be performed by connecting a plurality of cleaning devices in a merry-go-round manner at a constant time interval to one electrolytic reaction device. Note that two or more electrolytic reaction apparatuses may be provided with more cleaning apparatuses.

In the present invention, it is not necessary to interrupt the electrolytic treatment in the electrolytic reaction device or the cleaning treatment in the cleaning device for a long time, and continuous processing is possible depending on the balance between the time required for the electrolytic treatment and the cleaning treatment. , Processing efficiency is greatly improved.
The circulation line connected to the electrolytic reaction device and the cleaning device can be selected using appropriate selection switching means. As the selection switching means, a valve device such as a switching valve or an on-off valve can be used.

  Note that persulfuric acid has a higher self-decomposition rate and a higher peeling cleaning action as the temperature is higher. At a high temperature such as 130 ° C., the self-decomposition rate becomes very fast with a half-life of about 5 minutes. On the other hand, in the electrolytic reaction apparatus, the lower the solution temperature, the better the efficiency of producing persulfuric acid and the smaller the wear of the electrode. In the present invention, since the cleaning device and the electrolytic reaction device are separated, the temperature of the solution electrolyzed in the electrolytic reaction device can be kept lower than the temperature of the cleaning solution. Can increase the efficiency.

  The cleaning liquid can be heated to an appropriate temperature by appropriate heating means. Examples of the heating means include a heater, a heater utilizing heat exchange with hot water, steam, and the like, but the present invention is not limited to a specific one. The appropriate temperature of the cleaning liquid can be, for example, 100 ° C. to 150 ° C. Below this temperature range, the effect of stripping and cleaning with persulfuric acid decreases. On the other hand, when the temperature exceeds 160 ° C., the rate of self-decomposition of persulfuric acid becomes extremely high, and the resist and the like cannot be sufficiently oxidized.

Moreover, the solution electrolyzed by the electrolytic reaction apparatus can be cooled to an appropriate temperature by an appropriate cooling means. Examples of the cooling means include air coolers and water coolers. The appropriate temperature as the solution to be electrolyzed can be in the range of 10 to 90 ° C. When the temperature range is exceeded, the electrolysis efficiency decreases and the wear of the electrode also increases. On the other hand, if the temperature is below the above temperature range, the heat energy for heating the cleaning apparatus internal temperature to 130 ° C. becomes enormous, and the piping path for heat exchange becomes significantly longer, which is not practical. For the same reason, it is more desirable to set the lower limit to 40 ° C. and the upper limit to 80 ° C.
The heating means and cooling means described above may be attached to a cleaning device or an electrolytic reaction device, or may be provided in a circulation line. Further, another line may be provided in the cleaning device or the electrolytic reaction device to heat or cool the solution.

  The temperature of the solution to be electrolyzed can be adjusted by exchanging heat with each other when the solution is sent between the cleaning device and the electrolytic reaction device through a circulation line. That is, a persulfuric acid solution (return solution) that is relatively heated and sent from the cleaning device to the electrolytic reaction device, and a persulfuric acid solution that is relatively lowered in temperature and sent from the electrolytic reaction device to the cleaning device When the (feed liquid) is heat-exchanged with each other, the return liquid having a high temperature is deprived of heat by heat exchange, and the temperature is lowered, so that temperature adjustment desirable as an electrolysis solution of the electrolytic reaction apparatus is performed. The heat exchange can be performed by an appropriate heat exchange means such as a heat exchanger. Quartz and tetrafluoroethylene, which are not easily damaged by persulfuric acid, are desirable for the flow path material in the circulation line including the flow path of the heat exchanger. In addition to the heat exchange, it is possible to provide a means for cooling the solution to be electrolyzed.

  In the above system, the solution electrolyzed in the electrolytic reaction apparatus contains sulfate ions, and the production efficiency of persulfate ions in the electrolytic reaction apparatus is greatly influenced by the sulfuric acid concentration. Specifically, the persulfuric acid generation efficiency increases as the sulfuric acid concentration decreases. On the other hand, when the sulfuric acid concentration is lowered, the solubility of an organic compound such as a resist is lowered, and it is difficult to peel off the material to be cleaned. From these viewpoints, the sulfuric acid concentration of the solution used in the system is preferably in the range of 8M to 18M, for example. For the same reason, it is more desirable that the lower limit is 12M and the upper limit is 17M.

  In the electrolytic reaction apparatus, electrolysis is performed by pairing an anode and a cathode. The material of these electrodes is not limited to a specific one in the present invention. However, when platinum, which is widely used as an electrode, is used as the anode of the electrolytic reaction apparatus of the present invention, there is a problem that persulfate ions cannot be produced efficiently and platinum is eluted. On the other hand, the diamond electrode can efficiently generate persulfate ions and has little electrode wear. Therefore, among the electrodes of the electrolytic reaction apparatus, it is desirable that at least the anode that generates sulfate ions is composed of a diamond electrode, and it is more desirable that both the anode and the cathode are composed of diamond electrodes.

  The conductive diamond electrode is based on a semiconductor material such as a silicon wafer, and after synthesizing a conductive diamond thin film on the surface of the wafer, the wafer is melted or deposited and synthesized in a plate shape without using the base. Mention may be made of self-standing conductive polycrystalline diamond. In addition, a laminate formed on a metal substrate such as Nb, W, or Ti can be used. However, when the current density is increased, there is a problem that the diamond film is peeled off from the substrate.

Production of persulfate ions from sulfate ions using a conductive diamond electrode has been reported for a current density of about 0.2 A / cm ² (Ch. Cominellis et al., Electrochemical and Solid-State). Letters, Vol. 3 (2) 77-79 (2000), Special Table 2003-511555). However, an electrode having a diamond thin film supported on a metal substrate has a problem that the diamond film is peeled off and the effect disappears in a short period of time. Therefore, a self-supporting conductive diamond electrode in which the substrate is removed after being deposited on the substrate is desirable.

The conductive diamond thin film is a conductive thin film that is doped with a predetermined amount of boron or nitrogen during the synthesis of the diamond thin film, and is generally boron-doped. If the doping amount is too small, the technical significance does not occur. If the doping amount is too large, the doping effect is saturated. Therefore, a doping amount in the range of 50 to 20,000 ppm with respect to the carbon amount of the diamond thin film is suitable. .
In the present invention, the conductive diamond electrode is usually a plate-like one, but a network structure having a plate-like shape can also be used. That is, in the present invention, the shape and number of electrodes are not particularly limited.

In the electrolytic treatment performed using the conductive diamond electrode, the current density on the surface of the conductive diamond electrode is set to 10 to 100,000 A / m ^2, and a solution containing sulfate ions is parallel to the diamond electrode surface and the liquid passage speed is set. It is desirable to perform contact treatment at 1 to 10,000 m / h.

In the cleaning system of the present invention, cleaning processing can be performed on various materials to be cleaned, but cleaning processing is performed on electronic material substrates such as silicon wafers, glass substrates for liquid crystals, and photomask substrates. It is suitable for the use to do. More specifically, it can be used for a peeling process of an organic compound such as a resist residue attached on a semiconductor substrate. Further, it can be used for a foreign matter removing process such as fine particles and metal adhering to the semiconductor substrate.
Conventionally, prior to a cleaning process, a process for processing a semiconductor substrate usually includes a step of pre-oxidizing and ashing an organic resist using a dry etching or ashing process as a pre-processing step. Yes. This process has a problem of increasing the apparatus cost and the processing cost. By the way, in the system of the present invention, an excellent cleaning effect can be obtained. Therefore, even when a cleaning process is performed without incorporating a pretreatment process such as the above-described dry etching or ashing process, the resist is sufficiently removed. Is obtained. That is, the present invention makes it possible to establish a process in which these pretreatment steps are omitted.

  As described above, according to the operation method of the sulfuric acid recycling type cleaning system of the present invention, an electrolytic reaction device that generates persulfate ions from sulfate ions contained in the solution and regenerates the persulfate solution by an electrolytic reaction; A method for operating a sulfuric acid recycle type cleaning system comprising: a cleaning device for cleaning a material to be cleaned using a persulfuric acid solution as a cleaning liquid; and a circulation line for circulating the persulfuric acid solution between the electrolytic reaction device and the cleaning device. When cleaning the material to be cleaned by the cleaning device, the circulation of the persulfuric acid solution in the circulation line is stopped, and the electrolytic reaction is performed when the material to be cleaned is not cleaned by the cleaning device. Since the persulfuric acid solution was regenerated by electrolytic reaction in the apparatus, and the persulfuric acid solution was circulated between the electrolytic reaction apparatus and the cleaning apparatus by the circulation line, it was transferred to the cleaning liquid. Dyeing by can electrode of the electrolytic reactor to avoid the wasting. This eliminates the need for electrode replacement and delays the replacement time.

  Furthermore, by electrolytic reaction, an electrolytic reaction device that generates persulfate ions from sulfate ions contained in the solution to regenerate the persulfate solution, a plurality of cleaning devices that clean the material to be cleaned using the persulfate solution as a cleaning solution, An operation method of a sulfuric acid recycle type cleaning system comprising a plurality of circulation lines that individually connect an electrolytic reaction device and the plurality of cleaning devices to allow the persulfuric acid solution to circulate, respectively. In the cleaning device, the circulation of the persulfuric acid solution is stopped between the electrolytic reaction device, and at least one of the cleaning devices that does not clean the material to be cleaned is persulfuric acid by electrolytic reaction. If the persulfuric acid solution is circulated by a circulation line with the electrolytic reaction apparatus that is regenerating the solution, another cleaning apparatus can be used when cleaning the material to be cleaned by the cleaning apparatus. The solution is circulated between the electrolytic reaction apparatus can be reproduced persulfate solution by performing electrolysis, the effect of improving the processing efficiency in addition to the effect.

  In addition, according to the sulfuric acid recycling type cleaning system of the present invention, an electrolytic reaction device that generates persulfate ions from sulfate ions contained in the solution by an electrolytic reaction to regenerate the persulfate solution, and the persulfate solution as a cleaning solution. A plurality of cleaning devices for cleaning the cleaning material, a plurality of circulation lines that individually connect the electrolytic reaction device and the plurality of cleaning devices to allow the persulfuric acid solution to circulate, and a connection to the electrolytic reaction device Since the circulation line and the selection switching means for selectively switching the cleaning device are provided, the above-described operation method can be executed reliably and easily to obtain the above-described effect.

( Reference form )
Below, the reference form with respect to this invention is demonstrated based on FIG.
In the cleaning tank 1 corresponding to the cleaning apparatus in the present invention, electrolytic reaction tanks 10 a and 10 b constituting the electrolytic reaction apparatus 10 are connected by a return pipe 4 and a feed pipe 5. The return pipe 4 and the feed pipe 5 each have at least an inner surface made of tetrafluoroethylene, and a liquid feed pump 6 for feeding a persulfuric acid solution is interposed in the return pipe 4. The return pipe 4 and the feed pipe 5 are provided with on / off valves 40 and 50, respectively, and these on / off valves 40 and 50 open or close in conjunction with each other. The return pipe 4, feed pipe 5, the liquid feed pump 6, the circulation line is constituted. Between the return pipe 4 and the feed pipe 5, the heat exchanger 7, which corresponds to the heat exchange means is interposed, through the feed tube 5 with a solution flowing through the return pipe 4 by the heat exchanger 7 Heat exchange with the solution is possible. Note that at least the inner surface of the flow path (not shown) in the heat exchanger 7 is made of tetrafluoroethylene. As described above, the flow path of the return pipe 4, the feed pipe 5, and the heat exchanger 7 is made of tetrafluoroethylene or the like that is resistant to persulfuric acid, so that wear due to persulfuric acid can be avoided.

The electrolytic reaction tanks 10a and 10b are connected in series, the return pipe 4 is connected to the electrolytic reaction tank 10a, and the feed pipe 5 is connected to the electrolytic reaction tank 10b. A connecting pipe 15 is connected between the electrolytic reaction tank 10a and the electrolytic reaction tank 10b. That is, the return pipe 4, the electrolytic reaction tank 10 a, the connecting pipe 15, the electrolytic reaction tank 10 b, and the feed pipe 5 are passed in this order.
The electrolytic reaction tank 10a is provided with an anode 11a and a cathode 12a, and the electrolytic reaction tank 10b is provided with an anode 11b and a cathode 12b. Further, bipolar electrodes 13a... 13a are provided at a predetermined interval between the anode 11a and the cathode 12a. And the bipolar electrodes 13b... 13b are arranged at a predetermined interval between the anode 11b and the cathode 12b. Note that the electrolytic cell is not a bipolar type, and may include only an anode and a cathode as electrodes. In this reference form , these electrodes 11a, 11b, 12a, 12b, 13a, and 13b are constituted by diamond electrodes having a diameter of 15 cm, and each electrode is a set of 10 in each electrolytic reaction tank. The diamond electrode is manufactured by forming a diamond thin film on a substrate and doping boron in a range of preferably 50 to 20,000 ppm with respect to the carbon content of the diamond thin film. Further, it may be a self-supporting type by removing the substrate after forming the thin film. The anode 11a and the cathode 12a, and the anode 11b and the cathode 12b are connected in parallel to the DC power source 14, thereby enabling DC electrolysis in the electrolytic reaction tanks 10a and 10b. Here, the anode 11a and the cathode 12a, and the anode 11b and the cathode 12b may be connected to the DC power source 14 in series.
The washing tank 1 includes a heater 21 that heats the persulfuric acid solution 2 accommodated therein, and further includes an ultrapure water replenishment line 25 that replenishes the persulfuric acid solution 2 with ultrapure water.

Next, the operation of the sulfuric acid recycling type cleaning system having the above configuration will be described.
A high concentration sulfuric acid solution adjusted at a rate of 40 l of 98% concentrated sulfuric acid and 10 l of ultrapure water is accommodated in the washing tank 1, heated by the heater 21, and maintained at 130 ° C.
In the electrolytic reaction tanks 10a and 10b, when the anodes 11a and 11b and the cathodes 12a and 12b are energized by the DC power source 14, the bipolar electrodes 13a to 13b are polarized, and the anode and the cathode appear at predetermined intervals. The solution sent to the electrolytic reaction tanks 10a and 10b is passed between these electrodes. At this time, it is desirable to set the output of the liquid feed pump 6 so that the liquid flow rate is 1 to 10,000 m / h. In the above energization, it is desirable to control the energization so that the current density on the diamond electrode surface is 10 to 100,000 A / m ² .

When electricity is supplied to the solution in the electrolytic reaction tanks 10a and 10b, sulfate ions in the solution are oxidized to generate persulfate ions. The persulfuric acid solution 2 is fed from the feed pipe 5 to the washing tank 1, and a high-concentration persulfuric acid solution 2 is obtained in the washing tank 1. In the washing tank 1, since the solution circulates between the electrolytic reaction tanks 10a and 10b and is electrolyzed in the electrolytic reaction tanks 10a and 10b to generate persulfate ions, a high persulfate ion concentration is obtained. In addition, although this reference form demonstrated the process which manufactures persulfuric acid from a sulfuric acid at the time of starting, persulfuric acid may be prepared from the beginning. However, in terms of producing persulfuric acid on-site, it is advantageous to produce persulfuric acid using an electrolytic reactor.

  After the persulfuric acid concentration becomes sufficiently high as the cleaning liquid in the cleaning tank 1 is used for cleaning, the liquid feed pump 6 is stopped and the opening / closing valves 40 and 50 are closed, and the temperature of the persulfuric acid solution 2 serving as the cleaning liquid is increased. In a state where the temperature in the cleaning tank 1 is about 130 ° C., the semiconductor wafer 30 as a material to be cleaned is immersed in the cleaning tank 1 and cleaning is started. Then, in the cleaning tank 1, a high oxidation action is obtained by the self-decomposition of persulfate ions, and contaminants and the like on the semiconductor wafer 30 are effectively peeled off and transferred to the persulfate solution 2. Further, the contaminants transferred to the persulfuric acid solution 2 are further decomposed by the oxidizing action of persulfuric acid. If the cleaning is continued, the contaminants of the semiconductor wafer 30 are gradually removed, and the contaminants in persulfuric acid are gradually decomposed. The cleaning process in the cleaning tank 1 is stopped when these removals and decompositions are sufficiently performed.

  The persulfuric acid concentration in the washing tank 1 is reduced by self-decomposition by the above washing, and after the washing treatment, the on-off valves 40 and 50 are opened and sent to the electrolytic reaction tanks 10a and 10b by the liquid feed pump 6. The solution is subjected to an electrolytic reaction. Note that the end of the cleaning process may be in a state that can be regarded as substantially ended, and the above process may be started before the material to be cleaned is removed from the cleaning tank 1. In the electrolytic reaction tanks 10a and 10b, persulfate ions are generated from sulfate ions by the electrolytic reaction, and the concentration of persulfuric acid decreased by autolysis is increased to regenerate the persulfate solution. The regenerated persulfuric acid solution 2 is fed to the washing tank 1 through the feed pipe 5 and electrolyzed while circulating the persulfuric acid solution 2 between the washing tank 1 and the electrolytic reaction tanks 10a and 10b. The persulfuric acid concentration of the persulfuric acid solution 2 can be gradually increased.

Further, when the persulfuric acid solution 2 moves from the washing tank 1 toward the electrolytic reaction tank 10a, the persulfate solution 2 is moved in the electrolytic reaction tank 10b and moved through the feed pipe 5 when the return pipe 4 is moved. In the meantime, heat exchange is performed in the heat exchanger 7. The persulfuric acid solution 2 fed from the washing tank 1 is heated to about 130 ° C. so as to be suitable for washing. On the other hand, the persulfuric acid solution 2 fed from the electrolytic reaction tank 10b to the washing tank 1 has a temperature of about 40 ° C. When these persulfuric acid solutions 2 are heat-exchanged, the persulfuric acid solution 2 moving through the return pipe 4 is lowered to a temperature close to 40 ° C., whereas the persulfuric acid solution 2 moving through the feed pipe 5 is close to 130 ° C. Heated to temperature. The persulfuric acid solution 2 that is heat-exchanged by the heat exchanger 7 and moves through the return pipe 4 is then gradually cooled by natural cooling to a temperature of about 40 ° C. suitable for the electrolytic reaction. Incidentally, surely because lowering the temperature, water-cooling the electrolytic cell and attaching a cooling means for forcibly cooling such as by air cooling. The persulfuric acid solution 2 that is heat-exchanged by the heat exchanger 7 and moves through the feed pipe 5 is sent to the washing tank 1 and mixed with the persulfuric acid solution 2 remaining in the washing tank 1. When the temperature of the persulfuric acid solution 2 in the cleaning tank 1 has decreased, the temperature can be raised to an optimum temperature for cleaning by heating with the heater 21. As described above, the high-concentration sulfuric acid solution is cooled when being sent from the washing tank 1 to the electrolytic reaction tank 10a, and after being electrolyzed, it is heated when being returned from the electrolytic reaction tank 10b to the washing tank 1. The amount of heat that is cooled in this one cycle is almost equal to the amount of heat that is heated, so a highly efficient heat exchanger 7 is incorporated, and heat energy is applied from the outside for the amount of heat release, so that the persulfuric acid solution is efficiently Temperature adjustment can be performed. Note that, as described above, by maintaining the solution temperature in the cleaning device 1 high during electrolysis, after the regeneration of the persulfuric acid solution 2 is completed, the solution can be promptly used for cleaning.
By cleaning the semiconductor wafer 30 by the sulfuric acid recycling type cleaning system, it is effective to regenerate the persulfuric acid solution 2 by repeatedly using the sulfuric acid solution without the need for adding hydrogen peroxide or ozone. Washing can be continued. In addition, the consumption of electrodes in the electrolytic reaction apparatus can be reduced.

(Working-shaped state)
Next, an embodiment of the present invention will be described with reference to FIG. In addition, about the structure similar to a reference form , the same code | symbol is attached | subjected and the description is abbreviate | omitted or simplified.
In this embodiment, it has washing tanks 1a and 1b as washing apparatuses and an electrolytic reaction apparatus 10, and the electrolytic reaction apparatus 10 and the washing tank 1a are connected by a return pipe 4a and a feed pipe 5a, The electrolytic reaction apparatus 10 and the cleaning tank 1b are connected by a return pipe 4b and a feed pipe 5b. The cleaning tanks 1a and 1b have the same configuration as that of the cleaning tank 1 of the first embodiment, respectively, a heater (not shown) for heating the persulfuric acid solution, and an ultrapure for replenishing the persulfuric acid solution with ultrapure water. A water supply line (not shown) is provided.

  The electrolytic reaction apparatus 10 is configured by connecting two electrolytic reaction tanks in series in the same manner as shown in the first embodiment, and a DC power source (not shown) is connected to the two electrolytic reaction tanks. DC electrolysis is possible.

In the return pipes 4a and 4b, liquid feed pumps 6a and 6b for feeding the persulfuric acid solution 2 are interposed. The return pipe 4a and the feed pipe 5a are provided with on-off valves 40a and 50a, respectively, and the return pipe 4b and the feed pipe 5b are provided with on-off valves 40b and 50b. The on-off valve 40b and the on-off valve 50b open or close in conjunction with each other. The return pipe 4a, the feed pipe 5a, and the liquid feed pump 6a constitute one circulation line, and the return pipe 4b, the feed pipe 5b, and the liquid feed pump 6b constitute another circulation line. The on-off valves 40a, 40b, 50a, 50b constitute selection switching means for selecting and connecting the electrolytic reaction device, the circulation line, and the washing tank.
Further, heat exchangers 7a and 7b corresponding to the heat exchanging means of the present invention are interposed between the return pipe 4a and the feed pipe 5a and between the return pipe 4b and the feed pipe 5b, respectively. The solution flowing in the return pipe 4a and the solution flowing in the feed pipe 5a can exchange heat with each other by the heat exchanger 7a, and the solution flowing in the return pipe 4b and the solution flowing in the feed pipe 5b by the heat exchanger 7b Can exchange heat with each other.

Next, the operation of the cleaning system will be described.
At startup, a high concentration sulfuric acid solution adjusted at a ratio of 40 l of 98% concentrated sulfuric acid and 10 l of ultrapure water is accommodated in the washing tanks 1a and 1b, heated by a heater, and maintained at 130 ° C. Then, the on-off valves 40 a and 50 a are opened, and the solution pump 6 a is operated to circulate the solution between the electrolytic reaction device 10. On the other hand, on the washing tank 1b side, the on-off valves 40b and 50b are closed, and the solution feed pump 6b is stopped to stop the solution circulation.
In the electrolytic reaction device 10, when energized to the solution, sulfate ions in the solution undergo an oxidation reaction to generate persulfate ions. The persulfuric acid solution 2 is fed from the feed pipe 5a to the cleaning tank 1a, and a high-concentration persulfuric acid solution 2 is obtained in the cleaning tank 1a. In the washing tank 1a, the solution circulates between the electrolytic reaction tanks 10a and 10b and is electrolyzed in the electrolytic reaction apparatus 10 to generate persulfate ions, so that a high persulfate ion concentration is obtained (FIG. 2 ( a)).
In this case, when the persulfuric acid solution 2 moves from the washing tank 1a to the electrolytic reaction device 10 through the return pipe 4a, the persulfuric acid solution that is subjected to electrolytic treatment in the electrolytic reaction device 10 and moves through the feed pipe 5a. 2, heat exchange is performed in the heat exchanger 7 a as in the first embodiment.
Also in this embodiment, the amount of heat to be cooled and the amount of heat to be heated in this one cycle are substantially equal, so that the temperature of the persulfuric acid solution 2 can be adjusted efficiently.
In addition, as mentioned above, by maintaining the temperature in the washing tank 1 high during electrolysis, the concentration of the persulfuric acid solution 2 can be increased, and then the washing tank 1 can be quickly washed.

  In the cleaning tank 1a that has been highly persulfated to a concentration suitable for cleaning, cleaning of the semiconductor wafer 30 that is a material to be cleaned is started. At this time, the on-off valves 40a and 50a are closed and the liquid feed pump 6a is stopped. On the other hand, on the cleaning tank 1b side, the on-off valves 40b and 50b are opened, and the liquid feed pump 6b is operated to start solution circulation. In the electrolytic reaction apparatus 10, the sulfate ions in the solution are oxidized to generate persulfate ions as described above. The persulfuric acid solution 2 is fed from the feed pipe 5b to the cleaning tank 1b, and a high-concentration persulfuric acid solution 2 is obtained in the cleaning tank 1b. (FIG. 2 (b)). Therefore, even when the semiconductor wafer 30 has already been cleaned in the cleaning tank 1b and a solution with a reduced persulfuric acid concentration is stored, the solution is regenerated as the persulfuric acid solution 2 to a persulfuric acid concentration suitable for cleaning. Can be increased up to. In addition, heat exchange is also performed between the return pipe 4b and the feed pipe 5b by the heat exchanger 7b in the same manner as described above, so that an appropriate temperature adjustment of the persulfuric acid solution 2 is performed.

  Next, when the cleaning process in the cleaning tank 1a is completed, the semiconductor wafer 30 is taken out from the cleaning tank 1a, and the on-off valves 40b and 50b are closed to stop the liquid feed pump 6b, while the on-off valves 40a and 50a are opened. The liquid feed pump 6a is operated to circulate the solution between the cleaning tank 1a and the electrolytic reaction apparatus 10. In the cleaning tank 1b, the circulation of the solution is stopped, and cleaning is started by immersing a new semiconductor wafer 30. In the washing tank 1a, the regeneration treatment is performed until the persulfuric acid concentration suitable for washing is obtained by the electrolytic reaction by the electrolytic reaction apparatus 10 (FIG. 2C). The processing step shown in FIG. 2 (b) and the processing step shown in FIG. 2 (c) are repeated alternately, whereby the cleaning of the cleaning material and the regeneration of the persulfuric acid solution are performed efficiently.

Using the system shown in FIG. 2, high-concentration sulfuric acid solution adjusted at a ratio of 40 l of 98% concentrated sulfuric acid and 10 l of ultrapure water was heated and maintained at 130 ° C. in two cleaning tanks 1a and 1b. In the electrolytic reaction apparatus 10, two tanks incorporating 10 conductive diamond electrodes doped with boron (5,000 ppm) on a Si substrate having a diameter of 15 cm and a thickness of 1 mm were arranged in series. The two washing tanks and the electrolytic reaction apparatus are installed so that the solution can be circulated and stopped. The effective anode area for electrolysis is 30 (dm) ² , the current density is set to 30 A / (dm) ² , electrolysis is performed at 40 ° C., and the solution is circulated between the washing tank 1 a and the electrolysis reactor. It was carried out at a flow rate of 2 l / min (liquid passage speed 160 m / h). After carrying out the electrolysis for 10 minutes, it was confirmed that the persulfuric acid concentration in the washing tank 1a reached 1.5 g / l. Therefore, the solution circulation was stopped and the solution between the washing tank 1b and the electrolytic reaction apparatus 10 was stopped. In the cleaning tank 1a, 50 5-inch wafers with resist (TOC concentration: 10 [mg / sheet] × 50 [sheet] / 50 [l] = 10 [mg / l]) were immersed in the cleaning tank 1a. Although the solution was colored light brown only immediately after immersion in the wafer, it became transparent immediately and the TOC concentration was below the detection limit. Since the persulfuric acid concentration in the cleaning tank reached 1.5 g / l after electrolysis for 10 minutes in the cleaning tank 1b, the solution circulation was stopped and the solution circulation between the cleaning tank 1a and the electrolytic reaction apparatus 10 was performed. Started again. In the cleaning tank 1b, 50 5-inch wafers with resist were immersed. Although the solution was colored light brown only immediately after immersion in the wafer, it became transparent immediately and the TOC concentration was below the detection limit. In the above procedure, the washing tank 1a and the washing tank 1b are alternately connected to the electrolytic reaction apparatus 10 to circulate the solution, and 10 minutes is one cycle, and the wafers with resist are washed 50 cycles / cycle while switching the washing tank. Was repeated. Although it continued for 32 hours (the number of washed wafers was 9,600), the resist stripping dissolution effect of the high-concentration sulfuric acid solution was good, and the TOC concentration was kept below the detection limit.

(Comparative Example 1)
A solution containing 40 l of 98% concentrated sulfuric acid and 10 l of 35% hydrogen peroxide was heated and maintained at 130 ° C. in a single washing tank. The resist-coated wafer was immersed in this solution in the same immersion cycle as in Example 1 to perform resist dissolution. Up to the first 6 cycles (300 wafers to be cleaned), the solution turned brown immediately after immersion in the wafer, but became colorless and transparent in less than 10 minutes, and the TOC concentration was also a detection limit. However, for the next 50 sheets, the solution remained brown even after 10 minutes immediately after immersion, and a residual TOC concentration of 10 mg / l was observed. Therefore, 10 l of the solution in the washing tank was pulled out, 10 l of hydrogen peroxide solution was added, and the solution was heated and maintained at 130 ° C. The wafer immersion was continued again. Up to the first 2 cycles (100 wafers to be cleaned), the solution was colored brown immediately after immersion in the wafer, but became colorless and transparent in a little less than 10 minutes, and the TOC concentration became the detection limit. However, for the next 50 reasons, even after 10 minutes passed immediately after immersion, the solution remained brown and a residual TOC concentration of 10 mg / l was observed. Again, 10 l of the solution in the washing tank was withdrawn, and 10 l of hydrogen peroxide solution was additionally added. Although the wafer immersion was continued, when 50 wafers were immersed, the resist peeling dissolution effect was poor and the resist remained on the wafer even after 10 minutes. When the total number of processed wafers was 400, the entire solution had to be replaced.

It is a figure which shows the washing | cleaning system in the reference form with respect to this invention. It is a figure which shows the operation state in the washing | cleaning system in one Embodiment of this invention .

Explanation of symbols

1, 1a, 1b Washing tank 2 Persulfate solution 4, 4a, 4b Return pipe 5, 5a, 5b Feed pipe 6, 6a, 6b Liquid feed pump 7, 7a, 7b Heat exchanger 10 Electrolytic reactor 10a, 10b Electrolytic reaction Tank 11, 11a, 11b Anode 12, 12a, 12b Cathode 13 Bipolar electrode 14 DC power supply 21 Heater 25 Ultrapure water supply line 30 Semiconductor wafer

Claims (7)

  An electrolytic reaction device that regenerates a persulfate solution by generating persulfate ions from sulfate ions contained in the solution by an electrolytic reaction, a plurality of cleaning devices that wash a material to be cleaned using the persulfate solution as a cleaning solution, and the electrolytic reaction A plurality of circulation lines that allow the persulfuric acid solution to be circulated by individually connecting the apparatus and the plurality of cleaning apparatuses, a heating unit that heats the cleaning liquid on each of the plurality of cleaning apparatuses, and the electrolytic reaction apparatus A method for operating a sulfuric acid recycling type cleaning system comprising a cooling means for cooling the solution sent to a cleaning device, wherein a cleaning material is cleaned with a persulfate solution between the electrolytic reactor and the electrolytic reaction device. Circulation is stopped and at least one of the cleaning apparatuses that have not cleaned the material to be cleaned is circulated with the electrolytic reaction apparatus in which the persulfuric acid solution is regenerated by electrolytic reaction. The cleaning solution is maintained at a high temperature by the heating means on the side of the cleaning device that circulates the persulfuric acid solution by a line and at the time of regeneration, and the cooling device side by the cooling means. A method for operating a sulfuric acid recycling type cleaning system, wherein the temperature of the solution sent to the electrolytic reaction device is lowered. In the circulation line, heat exchange is performed between a relatively low temperature persulfuric acid solution feed from the electrolytic reaction device and a relatively high temperature persulfuric acid solution return from the cleaning device. The operating method of the sulfuric acid recycle type cleaning system according to claim 1 , wherein Regenerating the persulfuric acid solution until the persulfuric acid concentration reaches a predetermined concentration while circulating the persulfuric acid solution between the cleaning device and the electrolytic reaction device that have finished cleaning the material to be cleaned; The sulfuric acid recycle type cleaning according to claim 1 or 2 , wherein the step of cleaning the material to be cleaned is repeatedly performed in the cleaning device without circulating the persulfuric acid solution with the electrolytic reaction device. How to operate the system. The operating method of the sulfuric acid recycle type cleaning system according to any one of claims 1 to 3 , wherein at least an anode of the electrodes provided in the electrolytic reaction apparatus is a conductive diamond electrode. The operation of the cleaning system according to any one of claims 1 to 4 , wherein the conductive diamond electrode provided in the electrolytic reaction device is a self-supporting conductive diamond electrode obtained by laminating the substrate and then removing the substrate. Method. In the regeneration, the persulfuric acid concentration during electrolysis in the electrolytic reaction device is less than the persulfuric acid concentration [g /%] with respect to the organic carbon concentration (TOC) generated by washing in the washing device circulated and connected to the electrolytic reaction device. The operation method of the sulfuric acid recycle type cleaning system according to any one of claims 1 to 5 , wherein the operation is performed until the condition of l] / TOC concentration [g / l] = 10 to 1000 is satisfied.   An electrolytic reaction device that regenerates a persulfate solution by generating persulfate ions from sulfate ions contained in the solution by an electrolytic reaction, a plurality of cleaning devices that wash a material to be cleaned using the persulfate solution as a cleaning solution, and the electrolytic reaction A plurality of circulation lines that individually connect the apparatus and the plurality of cleaning apparatuses to allow the persulfuric acid solution to circulate, and a selection switching unit that selectively switches between a circulation line connected to the electrolytic reaction apparatus and the cleaning apparatus. , Heating means for heating the cleaning liquid on each cleaning device side, and cooling means for cooling the solution sent from the cleaning device to the electrolytic reaction device, the heating means being connected by the selection switching means The cleaning apparatus can heat the cleaning liquid, and the cooling means can cool the solution sent to the electrolytic reaction apparatus connected by the selection switching means to electrolyze the solution. Sulfuric acid recycle type cleaning system, characterized by the.

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