JP2012069974A - Cleaning liquid supply system and cleaning system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a persulfuric acid concentration of a solution supplied to a cleaning side by quickly measuring a persulfuric acid concentration produced in a cleaning liquid supply system.SOLUTION: The cleaning liquid supply system includes: an electrolytic reaction apparatus for generating a persulfate ion through an electrolytic reaction of a sulfuric acid solution; a circulation line for supplying the sulfuric acid solution containing the persulfate ion generated in the electrolytic reaction apparatus as part or whole of a cleaning liquid to a cleaning side, where a material is cleaned, and receiving the sulfuric acid solution used as the cleaning liquid which is returned from the cleaning side to supply part or whole of the sulfuric acid solution to the electrolytic reaction apparatus; a storage tank for storing the sulfuric acid solution to circulate the sulfuric acid solution to the electrolytic reaction apparatus, while admitting the sulfuric acid solution regulated to 10-90°C from the return side of the circulation line and feeding the sulfuric acid solution in the storage tank to the deliver side of the circulation line, where it is heated to 100-170°C to be supplied to the cleaning side; and a persulfuric acid concentration measuring apparatus for measuring a persulfuric acid concentration in the sulfuric acid solution in the storage tank.

Description

  The present invention can recycle persulfuric acid and use it for cleaning while repeatedly using a sulfuric acid solution when cleaning and separating contaminants attached to a silicon wafer or the like with a solution containing persulfuric acid and sulfuric acid having a high peeling effect. The present invention relates to a possible cleaning liquid supply system and a cleaning system.

  Wafer cleaning technology in the VLSI manufacturing process is a process of stripping and cleaning resist residues, fine particles, metals and natural oxide films, etc., in a mixed solution of concentrated sulfuric acid and hydrogen peroxide (SPM) or a solution in which ozone gas is blown into concentrated sulfuric acid. (SOM) is frequently used. It has been found that peroxides formed by oxidizing sulfuric acid with hydrogen peroxide or ozone are useful for cleaning. In SPM, it is necessary to replenish hydrogen peroxide water to make up for the amount of hydrogen peroxide that decomposes and decreases. Since it is diluted with water in hydrogen peroxide water, it is difficult to maintain the liquid composition constant, and the liquid is discarded and renewed every predetermined time or every specified number of treatment batches. For this reason, there is a problem that a large amount of chemicals must be stored.

One SOM does not dilute the liquid and can generally make the liquid renewal cycle longer than SPM. However, the generation efficiency of peroxide by ozone is low, and the cleaning effect is slightly inferior to SPM. In these methods, there is a limit to the concentration of peroxide to be generated, which leads to the limit of the cleaning effect.
The present inventors have invented and proposed a technique for continuously supplying persulfuric acid having a high cleaning effect in a continuous and large amount (see Patent Document 1). That is, we have developed and proposed a cleaning liquid supply system that continuously generates persulfuric acid by electrolytic treatment of sulfuric acid solution and recycles sulfuric acid.

JP 2006-114880 A

  In the cleaning liquid supply system proposed above, industrially, it is necessary to efficiently generate persulfuric acid and perform electrolysis without waste. For this purpose, it is necessary to sample the persulfuric acid concentration as appropriate and measure it with an analyzer such as ion chromatography. However, with such a measurement method, it takes a considerable amount of time to know the concentration of persulfuric acid produced by the electrolytic reaction, and it is difficult to operate under appropriate conditions in an operating state in a timely manner. is there.

  The present invention has been made against the background of the above circumstances, and it is possible to quickly and quickly measure the concentration of persulfuric acid in a sulfuric acid solution in the system, and thus to supply a cleaning liquid that can be operated under suitable conditions. An object is to provide a system and cleaning system.

That is, in the cleaning liquid supply system of the present invention, the invention according to claim 1 is an electrolytic reaction device that generates persulfate ions from sulfate ions contained in the sulfuric acid solution by an electrolytic reaction of the sulfuric acid solution, and the electrolytic reaction device. In the cleaning liquid supply system that enables the sulfuric acid solution containing persulfate ions generated in step 1 to be supplied to the cleaning side that cleans the material to be cleaned that is the electronic material substrate as part or all of the cleaning liquid,
The sulfuric acid solution used as the cleaning liquid returned from the cleaning side is received, a part or all of the sulfuric acid solution is supplied to the electrolytic reaction device, and the sulfuric acid solution electrolyzed in the electrolytic reaction device is supplied to the cleaning side. A circulation line for sending to the tank, and a storage tank for storing the sulfuric acid solution and circulating the sulfuric acid solution between the electrolytic reaction device,
In the storage tank, a sulfuric acid solution adjusted to 10 to 90 ° C. is introduced from the circulation line on the return side, and the sulfuric acid solution in the storage tank is sent to the circulation line on the delivery side to be 100 to 170. Heated to ℃ and supplied to the washing side,
A persulfuric acid concentration measuring device for measuring a persulfuric acid concentration in the sulfuric acid solution in the storage tank is provided.

  According to a second aspect of the present invention, there is provided a cleaning liquid supply system according to the first aspect, wherein the cleaning side performs peeling of an organic compound such as a resist residue attached to an electronic material substrate and oxidative decomposition of the organic compound. It is characterized by being.

  According to a third aspect of the present invention, there is provided the cleaning liquid supply system according to the first or second aspect, wherein the persulfuric acid concentration measuring device includes a conductive diamond electrode, and the conductive diamond electrode is provided in the cleaning liquid supply system. It arrange | positions so that it may contact with a sulfuric acid solution, It can measure the said persulfuric acid concentration in this sulfuric acid solution, It is characterized by the above-mentioned.

  According to a fourth aspect of the present invention, there is provided the cleaning liquid supply system according to the third aspect, wherein the persulfuric acid concentration measuring device is configured to measure a change in a current value when a potential scan is performed using the conductive diamond electrode as a working electrode. It is what is measured.

  According to a fifth aspect of the present invention, there is provided the cleaning liquid supply system according to the third aspect, wherein the persulfuric acid concentration measuring device measures a change in a current value with respect to a certain potential using the conductive diamond electrode as a working electrode. It is characterized by being.

  According to a sixth aspect of the present invention, there is provided a cleaning liquid supply system according to the third aspect, wherein the persulfuric acid concentration measuring device includes the conductive diamond electrode as a working electrode and a counter electrode.

  The invention of the cleaning liquid supply system according to claim 7 is the invention according to any one of claims 1 to 6, wherein at least the anode of the electrode used in the electrolytic reaction apparatus is a conductive diamond electrode. .

  The invention of the cleaning system according to claim 8 is the use of the cleaning liquid supply system according to any of claims 1 to 7 and a solution containing sulfuric acid and persulfuric acid supplied from the cleaning liquid supply system. And a cleaning device that performs cleaning and returns the cleaning liquid used for the cleaning to the cleaning liquid supply system.

That is, according to the cleaning liquid supply system of the present invention, the sulfuric acid solution containing persulfuric acid having a cleaning effect is supplied to the cleaning side to clean the material to be cleaned such as the electronic material substrate. In this cleaning, the contaminants attached to the electronic material substrate and the like are peeled off, removed, and oxidatively decomposed. Note that the sulfuric acid concentration of the cleaning liquid on the cleaning side is preferably 10 M or more as a concentration having a high peeling effect such as a resist. When the sulfuric acid concentration is less than 10M, the solubility of an organic compound such as a resist becomes low and it is difficult to peel off, and it is difficult to obtain a sufficient cleaning ability.
Further, the concentration of persulfuric acid contained in the sulfuric acid solution greatly affects the cleaning effect. In the present invention, the persulfuric acid concentration of the system can be measured by the persulfuric acid concentration measuring device, and the persulfuric acid concentration in the sulfuric acid solution supplied to the washing side can be appropriately adjusted and maintained based on this result.

  Furthermore, the temperature of the cleaning liquid on the cleaning side is preferably 100 ° C. to 170 ° C., for example. The sulfuric acid solution has a higher cleaning effect by raising the temperature, and 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 half-life of persulfate ions is about 5 minutes, and the self-decomposition rate becomes very fast, and an excellent cleaning action is exhibited. If the temperature of the cleaning solution is too low, the self-decomposition of persulfuric acid does not proceed sufficiently, and excellent cleaning performance is not exhibited. On the other hand, when the temperature of the cleaning liquid becomes excessively high, the decomposition rate of persulfuric acid becomes too fast, and the cleaning performance is deteriorated. Therefore, the temperature of the cleaning liquid on the cleaning side is preferably within the above range. The cleaning liquid may be heated at the cleaning liquid supply system so as to be supplied at an appropriate temperature for cleaning, or may be adjusted to an appropriate temperature by heating at the cleaning side. The cleaning liquid may be heated on both the cleaning liquid supply system side and the cleaning liquid supply system side.

  In the electrolytic reaction apparatus, electrolysis is performed using a sulfuric acid solution in which the concentration of persulfuric acid is reduced by the self-decomposition of persulfuric acid on the washing side. The sulfuric acid concentration of the solution to be subjected to the electrolytic reaction is preferably 1 to 6 M in order to increase the persulfuric acid production efficiency in the electrolysis process (persulfuric acid production ratio with respect to the passing current). If the sulfuric acid concentration is less than 1M, the average sulfuric acid concentration used on the washing side becomes low, so that a burden such as moisture reduction processing for adjusting the sulfuric acid concentration becomes large. On the other hand, when the sulfuric acid concentration exceeds 6M, the current efficiency in the electrolysis process decreases. In addition, since a suitable sulfuric acid concentration on the washing side is 10 M or more as described above, when a high-concentration sulfuric acid solution is supplied to the electrolysis reactor, it is diluted by adding water or the like to the above concentration. Is desirable. The water increased by this dilution can be offset by reducing the water in the sulfuric acid solution returned from the washing side.

  In the electrolytic reaction apparatus, persulfuric acid is generated by electrolyzing the sulfuric acid solution as described above to enhance the cleaning effect. In this electrolysis, the lower the solution temperature, the better the production efficiency of persulfuric acid and the smaller the electrode wear. Therefore, the electrolysis temperature when producing persulfuric acid is desirably 10 to 90 ° C, and more desirably 20 to 50 ° C. When the temperature range is exceeded, the electrolysis efficiency decreases and the wear of the electrode also increases. On the other hand, below the above temperature, the heat energy for heating the solution supplied to the cleaning side to a temperature suitable for cleaning becomes enormous.

  In addition, the sulfuric acid solution used by the washing | cleaning side is used for the sulfuric acid solution supplied to an electrolytic reaction apparatus. Since the solution on the washing side is subjected to washing at a relatively high temperature as described above, the sulfuric acid solution returned from the washing side is also usually at a high temperature. The high-temperature sulfuric acid solution is desirably cooled by an appropriate cooling means to a temperature suitable for the electrolysis. Examples of the cooling means include air coolers and water coolers. Moreover, when diluting and adjusting the density | concentration of a sulfuric acid solution as mentioned above, the density | concentration of a solution can be reduced and temperature can be lowered | hung by mixing relatively low temperature dilution water, such as normal temperature.

In the electrolytic reaction apparatus, electrolysis is performed with the anode and the cathode paired. The material of these electrodes is not limited to a specific material 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 conductive diamond electrode can efficiently generate persulfate ions and has little electrode wear. Therefore, among the electrodes of the electrolytic reaction apparatus, at least the anode that generates sulfate ions is preferably composed of a conductive diamond electrode, and it is more desirable that both the anode and the cathode are composed of a conductive diamond electrode.

Examples of the conductive diamond electrode include a semiconductor material such as a silicon wafer as a substrate, a conductive diamond thin film synthesized on the wafer surface, and a self-standing type conductive polycrystalline diamond deposited and synthesized in a plate shape. . In addition, it is possible to use a laminate on a metal substrate such as Nb, W, Ti, etc. Production of persulfuric acid from sulfuric acid using a conductive diamond electrode is performed when the current density is about 0.2 A / cm ^2. Have been reported (Ch. Comnnellis et al., Electrochemical and Solid-State Letters, Vol. 3 (2) 77-79 (2000), Special Table 2003-511555), an electrode having a diamond thin film supported on a metal substrate However, there was a problem that the diamond film was peeled off and the effect disappeared in a short period of time. Therefore, a conductive diamond electrode deposited on a conductive silicon 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, 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. .

The present invention is provided with a persulfuric acid concentration measuring device for measuring the concentration of persulfuric acid in the sulfuric acid solution in the cleaning liquid supply system. It is desirable to utilize the reaction that is performed. This makes it possible to quickly measure the persulfuric acid concentration in an extremely short time.
In the measurement, a change in current due to the reduction can be measured using a working electrode and a reference electrode. In addition to this, a counter electrode can be used to form a three-pole type. It is desirable to use a conductive diamond electrode as the working electrode. The conductive diamond electrode may be the same as the electrode used in the above-described electrolytic reaction apparatus, or may be a self-supporting type with the substrate removed. It may be an electrode. Although there is no restriction | limiting in particular in the magnitude | size of an electrode, It is desirable to have a liquid contact area of about 0.1-2 cm < ² >.

  Since the liquid contact target is in a high-concentration sulfuric acid solution, it is desirable to use a conductive diamond electrode for the reference electrode and the counter electrode. When scanning the working electrode voltage, the scanning speed is not particularly limited, but is preferably about 1 to 500 mV / s. As for the scanning width of the working electrode, it is desirable to scan from about 0 V to about −3 V using the conductive diamond electrode as a reference electrode. When a negative potential exceeding −3 V is applied, hydrogen generation becomes intense and overlaps with the reduction current of persulfuric acid, making measurement difficult. The current generated when persulfuric acid is reduced can be observed with a potentiostat, but even a weak current of about 100 nA can be detected with high accuracy.

  Regarding the measurement of the persulfuric acid concentration, the potential may be scanned as described above, but the transition of the reduction current may be observed while being fixed at a constant potential. The potential to be fixed is preferably selected to be about -1.5 to -2.5 V within a range of 0 to -3 V using a conductive diamond electrode as a reference electrode. As an operation, the potential is set to 0V, the potential is stepped to -2V, and the reduction current at that time is observed.

In the present invention, cleaning liquid can be supplied for various materials to be cleaned. However, the cleaning liquid can be supplied to electronic material substrates such as silicon wafers, glass substrates for liquid crystals, and photomask substrates. Is preferred. 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.
In addition, the present invention can be used in a process of cleaning and removing contaminants attached to a substrate such as a silicon wafer with a high-concentration sulfuric acid solution. The present invention relates to a system in which a persulfuric acid solution is produced on-site by an electrolytic reaction apparatus in order to increase the efficiency and a chemical solution such as hydrogen peroxide or ozone from the outside is not required by repeatedly using the sulfuric acid solution.

As described above, according to the cleaning liquid supply system of the present invention, the electrolytic reaction device that generates persulfate ions from the sulfate ions contained in the sulfuric acid solution by the electrolytic reaction of the sulfuric acid solution, and the electrolytic reaction device In a cleaning liquid supply system that enables supplying a sulfuric acid solution containing persulfate ions as a part or all of the cleaning liquid to a cleaning side that cleans a material to be cleaned that is an electronic material substrate,
The sulfuric acid solution used as the cleaning liquid returned from the cleaning side is received, a part or all of the sulfuric acid solution is supplied to the electrolytic reaction device, and the sulfuric acid solution electrolyzed in the electrolytic reaction device is supplied to the cleaning side. A circulation line for sending to the tank, and a storage tank for storing the sulfuric acid solution and circulating the sulfuric acid solution between the electrolytic reaction device,
In the storage tank, a sulfuric acid solution adjusted to 10 to 90 ° C. is introduced from the circulation line on the return side, and the sulfuric acid solution in the storage tank is sent to the circulation line on the delivery side to be 100 to 170. Heated to ℃ and supplied to the washing side,
Since it is equipped with a persulfuric acid concentration measuring device that measures the persulfuric acid concentration in the sulfuric acid solution in the storage tank, the persulfuric acid concentration in the sulfuric acid solution can be quickly measured during operation and used for control of the electrolysis reactor, etc. This makes it possible to obtain a reliable cleaning effect and further increase the operating efficiency.
By regenerating persulfuric acid by electrolysis while repeatedly using sulfuric acid, a cleaning solution having a high cleaning effect can be continuously supplied.

1 is a schematic configuration diagram illustrating a cleaning liquid supply system and a cleaning system according to an embodiment of the present invention. Similarly, it is a figure which shows a persulfuric acid concentration measuring apparatus. It is a graph which shows the relationship between the scanning electric potential in an Example, and the measured reduction current. Similarly, it is a graph showing the correlation between the reduction current and the persulfuric acid concentration.

Below, one Embodiment of this invention is described based on FIG.
The cleaning tank 1 for cleaning the semiconductor wafer 5 is connected to the cleaning liquid introduction path 2 and the cleaning liquid return path 3, and the cleaning liquid introduction path 2 can be connected to the cleaning liquid supply path 16 of the cleaning liquid supply system 10. The cleaning liquid return flow path 3 can be connected to the sulfuric acid solution return flow path 11 of the cleaning liquid supply system 10 via the pump 4. The cleaning system of the present invention is configured by connecting the cleaning tank 1 and the cleaning liquid supply system 10.

  In the cleaning liquid supply system 10, the downstream side of the sulfuric acid solution return flow path 11 is branched into a circulation branch path 11 b and a water reduction branch path 11 a, and the circulation branch path 11 b includes a heater 14 for heating the cleaning liquid and A filter 15 is interposed, and is connected to the cleaning liquid supply path 16 by joining a persulfuric acid solution feeding path 38 described later on the downstream side thereof.

  On the other hand, the water reducing branch 11a is connected to the tower top of a diffusion tower 20 (gas stripping device) which is a solution moisture reducing means on the downstream side. The diffusion tower 20 is filled with a filler (not shown) such as a glass Raschig ring, and a solution that flows through the filler from the top of the tower by introducing diffusion air from the lower side and a filler from the lower side. The air rising through it is counterflowed to evaporate some of the water in the solution and taken up into the rising air and discharged with the outlet gas. The solution with reduced water content is taken out from the bottom of the stripping tower 20 to the drain 21. The drainage channel 21 is provided with a pump 22, and the downstream side is branched into an electrolysis branch channel 21 a and a circulation branch channel 21 b, and the circulation branch channel 21 b is connected to the circulation branch channel 11 b described above. Have joined.

The electrolysis branch path 21 a is connected to a first storage tank 25, and a diluted water feed path 26 is connected to the first storage tank 25. Further, a delivery path 27 is connected to the first storage tank 25, and the delivery path 27 is branched into an electrolysis branch path 27 a and a circulation branch path 27 b via a pump 28. The circulation branch 27 b is circulated and connected to the first storage tank 25 through the heat exchanger 29.
The electrolysis branch path 27a is connected to the second storage tank 30, and the electrode section 41 of the persulfuric acid concentration measuring device 40 shown in FIG. The electrode portion 41 is composed of a rod 41d made of polytetrafluoroethylene and a working electrode 41a, a reference electrode 41b, and a counter electrode 41c each made of a conductive diamond electrode. The liquid is brought into contact with the sulfuric acid solution in the second storage tank 30 and used for measuring the concentration of persulfuric acid. Each of the electrodes is connected to a potentiostat 42 to constitute a persulfuric acid concentration measuring device 40.
Each working electrode 41a, reference electrode 41b, and counter electrode 41c may be arranged on a flat plate on the tip surface of the rod 41d, as shown in FIG. 2 (b), or as shown in FIG. 2 (c). Thus, in order to increase the reaction efficiency, for example, the working electrode 41a and the counter electrode 41c are protruded downward to face each other, and the reference electrode 41b can be disposed on a flat plate. In addition, it is desirable that the electrode protruded downward is covered with polytetrafluoroethylene 41e or the like that is resistant to persulfuric acid except for the opposing surface (back side and bottom side).

In addition, a delivery path 32 is connected to the second storage tank 30, and a switching valve 34 is connected to the delivery path 32 via a pump 33. An electrolysis feed path 35 is connected to one port of the switching valve 34, and a persulfuric acid solution supply path 38 is connected to the other port of the switching valve 34. The persulfuric acid solution supply path 38 joins with the circulation path 11 b and is connected to the cleaning liquid supply path 16.
On the other hand, the downstream end of the electrolytic feed path 35 is connected to the liquid inlet side of the electrolytic reaction tank 36 included in the electrolytic reaction apparatus, and the electrolytic return path 37 is connected to the liquid discharge side of the electrolytic reaction tank 36. The electrolytic return path 37 is connected to the second storage tank 30.

In the electrolytic reaction tank 36, an anode 36a and a cathode 36b are disposed, and a bipolar electrode 36c is disposed between the anode 36a and the cathode 36b, if desired, with a predetermined interval. It is also possible to configure the electrolytic reaction tank without a bipolar electrode. A direct current power source (not shown) is connected to the anode 36a and the negative electrode 36b, and direct current electrolysis of the solution in the electrolytic reaction tank 36 is enabled by energizing the direct current power while passing the solution between the electrodes. Yes. In this embodiment, the electrode is composed of a conductive diamond electrode. The conductive 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.
An electrolytic reaction apparatus is constituted by the electrolytic reaction tank 36 including the electrodes described above and a DC power source (not shown).
Further, the circulation line of the present invention is constituted by each path in the cleaning liquid supply system.

Next, the operation of the cleaning liquid supply system and the cleaning system configured as described above will be described.
A sulfuric acid solution having a sulfuric acid concentration of 10 M or more (for example, about 75% by mass) is accommodated in the cleaning tank 1. The sulfuric acid solution is heated to 100 to 170 ° C. and used for cleaning the semiconductor wafer 5. The cleaning liquid is sequentially returned to the cleaning liquid supply system 10 through the cleaning liquid return channel 3 by the pump 4. The returned sulfuric acid solution is introduced into the sulfuric acid solution return flow path 11, and a part thereof is distributed to the water reduction branch path 11 a as needed, and the rest is distributed to the circulation branch path 11 b.

  The sulfuric acid solution distributed to the water reducing branch 11a is introduced to the top of the stripping tower 20 and flows down in the filler. On the other hand, diffusion air supplied from a clean room or the like from the lower side is introduced into the diffusion tower 20 to rise in the filler, and a part of the water of the sulfuric acid solution is reduced by transpiration, and moves to the drainage channel 21. To do. The sulfuric acid solution that has moved to the drainage channel 21 has an increased sulfuric acid concentration due to the reduction of moisture, and the temperature has decreased due to contact with the air for diffusion and evaporation of moisture. On the other hand, the air stripped of moisture in the diffusion tower 20 is exhausted as an outlet gas. The concentrated sulfuric acid solution in the drainage channel 21 is fed by the pump 22, and a part thereof is distributed to the first storage tank 25 through the electrolysis branch channel 21 a as necessary, and the remainder is used for circulation through the circulation branch channel 21 b. It merges with the branch path 11b and is mixed with the sulfuric acid solution flowing through the branch path 11b for circulation. After the mixed solution in the circulation branch 11b is returned from the washing tank 1, the temperature is lowered, and this is heated by the heater 14 to 100 ° C. to 170 ° C. suitable for washing. Further, since solid suspended matter (SS) or the like may be mixed in the solution by the cleaning in the cleaning tank 1, the solid content is removed by the filter 15 and supplied to the cleaning liquid supply path 16.

On the other hand, in the first storage tank 25, a relatively high-temperature high-concentration sulfuric acid solution is supplied through the branching path 21 a for electrolysis, and dilution water is supplied through the dilution water supply path 26. In the 1st storage tank 25, it adjusts to the sulfuric acid concentration of 1-6M suitable for the electrolysis in the electrolytic reaction tank 36 by maintaining the mixing ratio of a high concentration sulfuric acid solution and dilution water appropriately. At this time, the temperature of the solution can be lowered by mixing relatively low-temperature dilution water.
The sulfuric acid solution in the first storage tank 25 is sent to the delivery path 27 by the pump 28 when the time is not required for electrolysis, and the whole amount is sent to the circulation branch path 27b and cooled by the heat exchanger 29. The first storage tank 25 is returned. By repeating this and circulating the sulfuric acid solution, the temperature of the sulfuric acid solution is adjusted to 10 to 90 ° C. suitable for the electrolytic reaction. When the sulfuric acid solution is electrolyzed, the circulation is stopped, and the sulfuric acid solution is transferred to the second storage tank 30 by the pump 28 through the delivery path 27 and the electrolysis branch path 27a. The sulfuric acid solution accommodated in the second storage tank 30 is fed by the pump 33 through the delivery path 32 during electrolysis. The delivery path 32 is communicated with the electrolysis delivery path 35 by a switching valve 34. As a result, the sulfuric acid solution is sent to the electrolytic feed path 35 and supplied to the electrolytic reaction tank 36. In the electrolytic reaction tank 36, during the electrolysis, the anode 36a and the cathode 36b are energized by a DC power source, and the bipolar electrode 36c is polarized. The sulfuric acid solution fed to the electrolytic reaction tank 36 is electrolyzed while passing water between the electrodes. At this time, it is desirable to set the linear velocity of liquid to be 1 to 10,000 m / hr. In the energization, it is desirable to control the energization so that the current density on the surface of the conductive diamond electrode is 10 to 100,000 A / m ² .

  When the sulfuric acid solution is energized in the electrolytic reaction tank 36, the sulfuric acid ions in the sulfuric acid solution undergo an oxidation reaction to generate persulfate ions, and the persulfuric acid solution can be obtained efficiently. The persulfuric acid solution obtained in the electrolytic reaction tank 36 is returned to the second storage tank 30 through the return path 37 for electrolysis, and further sent through the feed path 36 for electrolysis, so that the sulfuric acid solution is supplied to the second storage tank 30. The persulfuric acid having a high concentration can be generated by electrolysis while circulating between the electrolytic reaction tank 36 and the electrolytic reaction tank 36. In addition, since the temperature of the persulfuric acid solution is increased by the electrolysis, the persulfuric acid solution may be cooled as necessary in the electrolysis feed path 36, the electrolysis return path 37, or the like.

  In the second storage tank 30, the persulfuric acid concentration in the sulfuric acid solution is measured by the persulfuric acid concentration measuring device 40 at appropriate times, for example, intermittently at predetermined time intervals. In this measurement, the voltage applied to the working electrode 41a as a potential with respect to the reference electrode 41b is scanned in the range of 0 to -3V (preferably -1.5 to -2.5V), and the reduction current is measured with the potentiostat 42. To do. By associating the obtained current value and the persulfuric acid concentration in advance, the persulfuric acid concentration in the sulfuric acid solution can be known. When the persulfuric acid concentration reaches a predetermined value, it is determined that the supply to the cleaning side is possible, the electrolysis is stopped, the switching valve 34 is switched, and the delivery path 32 and the persulfuric acid solution supply path. 38 is communicated. The sulfuric acid solution whose persulfuric acid concentration is sufficiently increased by the operation of the pump 33 is sent from the second storage tank 30 to the cleaning liquid supply path 16 through the delivery path 32 and the persulfuric acid solution supply path 38. Thereby, a cleaning solution having a persulfuric acid concentration exceeding a predetermined value is always supplied to the cleaning side, and a stable cleaning effect can be brought about. Further, in the electrolytic reaction tank 36, electrolysis is not performed more than necessary, and an efficient operation is possible.

In the washing tank 1, a high concentration sulfuric acid solution is supplied in a state containing a high concentration of persulfuric acid. The cleaning liquid in the cleaning tank 1 effectively strips and removes the resist adhering to the semiconductor wafer by high concentration, sulfuric acid, and high oxidizing power due to self-decomposition of persulfate ions, and further oxidatively decomposes. In the cleaning liquid, the persulfate ion concentration decreases due to autolysis. However, the cleaning liquid is returned to the cleaning liquid supply system 10 through the cleaning liquid return channel 3 as described above, and a part of the cleaning liquid is efficiently electrolyzed in the electrolytic reaction tank 36 to regenerate persulfuric acid having a predetermined concentration. Supplied to the cleaning solution. For this reason, the persulfate ion concentration in the washing tank 1 can be maintained moderately. In addition, the cleaning liquid is circulated and supplied to the cleaning tank, except for electrolysis, and in part, the moisture is reduced and the persulfuric acid concentration is increased and supplied again to the cleaning liquid. The added amount of dilution water is offset, and the sulfuric acid concentration of the cleaning liquid in the cleaning tank 1 is maintained at a high concentration suitable for cleaning.
That is, according to the present embodiment, a high-concentration sulfuric acid solution is electrolyzed to produce persulfuric acid, and the production amount is continuously and rapidly monitored. The attached contaminants, mainly organic substances, can be peeled off and oxidized for a long time.

  As mentioned above, although this invention was demonstrated based on the said embodiment, the said embodiment is one form of this invention, This content does not limit this invention. For example, even when electrolyzing a high-concentration sulfuric acid solution as it is without concentrating the sulfuric acid solution or diluting with water in the electrolysis step, the persulfuric acid concentration in the sulfuric acid solution can be quickly grasped by the persulfuric acid concentration measuring device of the present invention. Also, the present invention can be carried out when electrolysis is performed without circulating the electrolytic solution.

Using the cleaning system of the above embodiment, a high-concentration sulfuric acid solution prepared at a ratio of 34 liters of 97% concentrated sulfuric acid and 21 liters of ultrapure water was prepared in a cleaning tank and heated to 150 ° C. In the cleaning tank, a 12-inch silicon wafer with a resist was immersed in 50 sheets / cycle in a 10-minute immersion cycle to dissolve the resist. A part of this solution was extracted and sent to the stripping tower, and ultrapure water was added in the first storage tank to obtain a 4M sulfuric acid solution. After cooling this solution to 40 degreeC with a heat exchanger, it sent to the 2nd storage tank, was circulated between electrolytic reaction apparatuses, and raised the persulfuric acid density | concentration. In the electrolytic reaction apparatus, two tanks in which ten conductive diamond electrodes doped with boron on a conductive Si substrate of 12 × 12 cm and a thickness of 3 mm were incorporated were arranged in series in two tanks. Effective anode area for electrolysis is 18dm ^2, by setting the current density to 100A / dm ^2, and electrolysis at 40 ° C.. It was made to circulate with the flow volume of 2 l / min with the liquid feeding pump between the 2nd storage tank and the electrolytic reaction apparatus. In the second storage tank, a potential current curve was measured intermittently five times with a persulfuric acid concentration measuring device using the conductive diamond electrode as a reference electrode. At the same time, the persulfuric acid concentration was measured by oxidation-reduction titration using potassium iodide. Among them, a 4M sulfuric acid solution (persulfuric acid concentration 0 g / L) before electrolysis and a sulfuric acid solution having a maximum persulfuric acid concentration (180 g / L) obtained by electrolysis of a 4M sulfuric acid solution are shown in FIG. It was shown to.

As shown in FIG. 3, it can be seen that the sulfuric acid solution (solid line) having the maximum persulfuric acid concentration flows in the reduction direction as compared with 4M sulfuric acid (dashed line) in which no persulfuric acid exists.
Then, the absolute value of the reduction current in the vicinity of -1.7 V was read on the potential-current curve of all five data. A good correlation was recognized between the persulfuric acid concentration and the absolute value of the reduction current as shown in FIG. It can be seen that as the concentration of persulfuric acid increases, the reduction current increases approximately linearly.
A reduction current of 75 mA (current density was 15 mA / cm ² ) was observed near −1.7 V. From this current value, it was found that the persulfuric acid concentration reached 150 g / L. Therefore, the valve was switched, and the high-concentration persulfuric acid solution was sent to the washing tank to clean the silicon wafer with resist. Such wafer cleaning was continued for 8 hours (the number of cleaning wafers was 2,400). When the wafer was appropriately extracted and the organic residue on the wafer was analyzed with a mass spectrometer, the amount of organic substance was about 200 pg / cm ² . Thus, the resist stripping effect of the high-concentration sulfuric acid solution was good. Therefore, it continued for another 32 hours (9,600 cleaning wafers, 12,000 total processing wafers), but the resist stripping effect of the high-concentration sulfuric acid solution was good.

(Comparative example)
The silicon wafer with resist was cleaned in the same manner as in the above example except that no persulfuric acid monitor was installed. The concentration of persulfuric acid produced by the electrolytic reaction could not be quickly analyzed, the valve switching timing could not be determined, and the wafer cleaning effect varied.

DESCRIPTION OF SYMBOLS 1 Cleaning tank 10 Cleaning liquid supply system 11 Sulfuric acid solution return flow path 16 Cleaning liquid supply path 25 1st storage tank 26 Diluted water liquid supply path 27 Delivery path 30 Second storage tank 34 Switching valve 35 Electrolytic feed path 36 Electrolysis reaction tank 36a Anode 36b Cathode 36c Bipolar electrode 37 Return path for electrolysis 38 Persulfuric acid solution supply path

Claims (8)

An electrolytic reaction device that generates persulfate ions from sulfate ions contained in the sulfuric acid solution by electrolytic reaction of the sulfuric acid solution, and a sulfuric acid solution containing persulfate ions generated in the electrolytic reaction device as a part or all of the cleaning liquid In the cleaning liquid supply system that enables supply of the material to be cleaned to the cleaning side for cleaning,
The sulfuric acid solution used as the cleaning liquid returned from the cleaning side is received, a part or all of the sulfuric acid solution is supplied to the electrolytic reaction device, and the sulfuric acid solution electrolyzed in the electrolytic reaction device is supplied to the cleaning side. A circulation line for sending to the tank, and a storage tank for storing the sulfuric acid solution and circulating the sulfuric acid solution between the electrolytic reaction device,
In the storage tank, a sulfuric acid solution adjusted to 10 to 90 ° C. is introduced from the circulation line on the return side, and the sulfuric acid solution in the storage tank is sent to the circulation line on the delivery side to be 100 to 170. Heated to ℃ and supplied to the washing side,
A cleaning liquid supply system comprising a persulfuric acid concentration measuring device for measuring a persulfuric acid concentration in a sulfuric acid solution in the storage tank.   The cleaning liquid supply system according to claim 1, wherein the cleaning side performs peeling of an organic compound such as a resist residue attached to the electronic material substrate and oxidative decomposition of the organic compound.   The persulfuric acid concentration measuring device includes a conductive diamond electrode, the conductive diamond electrode is disposed so as to be in contact with the sulfuric acid solution in a cleaning liquid supply system, and measures the persulfuric acid concentration in the sulfuric acid solution. The cleaning liquid supply system according to claim 1 or 2, wherein   4. The cleaning liquid supply system according to claim 3, wherein the persulfuric acid concentration measuring device measures a change in current value when potential scanning is performed using the conductive diamond electrode as a working electrode.   4. The cleaning liquid supply system according to claim 3, wherein the persulfuric acid concentration measuring device measures a change in a current value with respect to a certain potential using the conductive diamond electrode as a working electrode.   The cleaning liquid supply system according to claim 3, wherein the persulfuric acid concentration measuring device includes the conductive diamond electrode as a working electrode and a counter electrode.   The cleaning liquid supply system according to any one of claims 1 to 6, wherein at least an anode of an electrode used in the electrolytic reaction apparatus is a conductive diamond electrode.   The cleaning liquid supply system according to any one of claims 1 to 7 and a solution to be cleaned are cleaned using a solution containing sulfuric acid and persulfuric acid supplied from the cleaning liquid supply system, and the cleaning liquid used for the cleaning is used. A cleaning system comprising: a cleaning device that returns to the cleaning liquid supply system.

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