JP4600666B2 - Sulfuric acid recycle type single wafer cleaning system - Google Patents

Description

  The present invention relates to a persulfuric acid solution while repeatedly using a sulfuric acid solution when cleaning and peeling off a contaminant such as a silicon wafer or other contaminants such as a resist that has become unnecessary with a persulfuric acid solution having a high peeling effect. The present invention relates to a sulfuric acid recycle type single wafer cleaning system that recycles and uses it for cleaning.

In a technique for cleaning an electronic material substrate such as a silicon wafer, a liquid crystal glass substrate, and a photomask substrate, a mixed solution (SPM) of concentrated sulfuric acid and hydrogen peroxide solution is usually used in a process of peeling and cleaning the resist. It has been found that the cleaning effect of SPM lies in the high oxidation resolution of persulfuric acid produced by hydrogen peroxide oxidizing sulfuric acid.
By the way, in SPM, it is necessary to replenish hydrogen peroxide water in order to compensate for the decomposition of persulfuric acid generated by hydrogen peroxide when it decomposes itself and its oxidizing power decreases. However, since the sulfuric acid concentration is gradually diluted by the addition of hydrogen peroxide solution, it is difficult to maintain the liquid composition constant, and the cleaning liquid is discarded and updated every predetermined time or every predetermined processing amount. Therefore, there is a problem that a large amount of chemicals must be stored and discarded. In this method, there is a limit to the concentration of persulfuric acid produced, which has led to the limit of the cleaning effect.
On the other hand, conventional apparatuses for performing resist stripping include a batch type apparatus that processes a plurality of substrates at once and a single wafer type apparatus that processes substrates one by one. Batch-type resist stripping equipment is equipped with a tank for immersing a plurality of substrates in resist stripping solution at a time, and because of the large equipment size and inferior cleaning ability compared to single wafer processing, the substrate to be processed recently With the increase in size, single-wafer type resist stripping apparatuses have attracted attention.

As a prior art relating to a single wafer cleaning apparatus, for example, in Patent Document 1, a cleaning liquid is supplied to a stage that rotates while holding a single substrate substantially horizontally, and the surface of the substrate held by this stage. A cleaning apparatus including a hopper is disclosed. A cleaning liquid supply means and a gas supply means are connected to the hopper. In the hopper, a jet of cleaning liquid droplets is formed by spraying the high pressure gas supplied from the gas supply means to the cleaning liquid supplied from the cleaning liquid supply means. In the form of a two-fluid spray nozzle that supplies the jet to the substrate surface. Further, Patent Document 2 discloses a resist stripping method and a resist stripping apparatus that satisfactorily remove a resist film using sulfuric acid and hydrogen peroxide solution as a resist stripping solution supplied to a single wafer cleaning apparatus.
Japanese Patent No. 3415670 JP 2004-172493 A

However, in the single wafer cleaning apparatus described above, since the cleaning liquid is used in a transient manner, a large amount of cleaning liquid is required when the number of cleaning sheets is large, and a large amount of sulfuric acid or hydrogen peroxide solution is stored or stored accordingly. There is a problem that it must be discarded.
The present invention has been made against the background of the above circumstances, and by reusing sulfuric acid by regenerating sulfuric acid by electrochemical action from an aqueous solution of sulfuric acid while repeatedly using sulfuric acid, the amount of sulfuric acid used is greatly reduced. An object of the present invention is to provide a sulfuric acid recycling type single wafer cleaning system.

That is, in the sulfuric acid recycle type single wafer cleaning system of the present invention, the first invention is to remove the resist on the substrate by cleaning the electronic material substrate using a persulfuric acid solution heated to 100 ° C. or more as a cleaning liquid. Persulfate ions are generated from sulfate ions contained in a solution having a sulfuric acid concentration in the range of 8M to 18M and a temperature in the range of 40 ° C to 90 ° C by a single wafer cleaning device and electrolytic reaction. An electrolytic reaction device for regenerating the persulfuric acid solution, and circulating the solution while performing the cleaning and the electrolysis between the cleaning device and the electrolytic reaction device, and a common solution storage tank is interposed between the feed side and the return side. And a circulation line provided .

The sulfuric acid recycle type single wafer cleaning system according to the second invention is characterized in that, in the first invention, a heating device is provided which sets the temperature of the cleaning liquid to 100 to 150 ° C.

The sulfuric acid recycle type single wafer cleaning system of the third invention is characterized in that, in the first or second invention, at least an anode of an electrode used in the electrolytic reaction apparatus is a conductive diamond electrode .

The sulfuric acid recycle type single wafer cleaning system according to a fourth aspect of the present invention is the first to third aspects of the invention, wherein the electrolytic reaction device is (persulfuric acid production rate [g / l / hr]) / (electrolytic reaction from the cleaning device). Electrolysis is performed such that the total organic carbon concentration (TOC) increase rate [g / l / hr]) of the solution fed to the apparatus satisfies 10 to 500.

A sulfuric acid recycle type single wafer cleaning system according to a fifth aspect of the present invention is the first to fourth aspects of the invention, further comprising a heat exchanger for exchanging heat between the solution on the feed side and the solution on the return side of the circulation line. And the solution storage tank is interposed on the side of the electrolytic reaction apparatus with respect to the heat exchanger .

A sulfuric acid recycle type single wafer cleaning system according to a sixth aspect of the present invention is the first to fifth aspects of the invention, wherein the single wafer type cleaning device is a liquid that mixes a cleaning liquid and a gas to form a jet of droplets of the cleaning liquid. It is provided with a droplet jet forming device .

According to a seventh aspect of the present invention, there is provided a sulfuric acid recycling type single wafer cleaning system according to the first to sixth inventions, wherein the single wafer cleaning device includes a substrate holding means for holding a material to be cleaned that receives a droplet jet of the cleaning liquid. It is characterized by providing .

The sulfuric acid recycle type single wafer cleaning system according to an eighth aspect of the present invention is the electronic material substrate according to the first to seventh aspects, wherein the electronic material substrate is used for the cleaning without undergoing a pretreatment step in which the resist is oxidized and ashed in advance. It is characterized by being.

The sulfuric acid recycling type single wafer cleaning method of the ninth invention is a method of cleaning the electronic material substrate by a single wafer method using a persulfuric acid solution at 100 ° C. or higher as a cleaning liquid to remove the resist on the substrate, and by electrolytic reaction, Regenerating a persulfate solution by generating a persulfate ion from sulfate ions having a sulfuric acid concentration in the range of 8M to 18M and having a temperature in the range of 40 ° C to 90 ° C; The solution in the electrolytic reaction is circulated through a common liquid storage on the feed side and the return side while performing the washing and the electrolysis.

  According to the present invention, persulfate ions in the cleaning liquid self-decompose to generate an oxidizing power, and the contaminants of the material to be cleaned that are treated one by one are effectively peeled and cleaned by this oxidizing power. In the cleaning liquid, the persulfuric acid concentration gradually decreases due to self-decomposition of persulfate ions in the solution. This persulfuric acid solution is sent to the electrolytic reactor through a circulation line. In an electrolytic reactor, the anode and cathode are immersed in a solution containing sulfate ions, and current is passed between the electrodes to conduct electrolysis, whereby sulfate ions are oxidized to produce persulfate ions, and the persulfate concentration is sufficiently high. Regenerated to solution. The regenerated persulfuric acid solution is returned to the cleaning device through the circulation line, and the material to be cleaned is effectively peeled and cleaned with a high concentration of persulfuric acid in the same manner as described above. The persulfuric acid solution can be continuously circulated between the cleaning device and the electrolytic reaction device, so that effective cleaning can be continued while maintaining the persulfuric acid composition. At the time of start-up, circulation of the persulfuric acid solution can be started by preparing sulfuric acid and sending it to the washing device as a persulfuric acid solution in the electrolytic reaction device.

  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. For this reason, the cleaning liquid can be heated to an appropriate temperature by an appropriate heating means before the droplets are formed. 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 large and the resist cannot be sufficiently oxidized, so that the appropriate temperature of the cleaning liquid is within the above range.

  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. An appropriate electrolysis temperature for producing persulfuric acid is 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. If the temperature is lower than the above temperature, the heat energy for heating the cleaning liquid to an appropriate temperature 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.

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.
Also, in order to raise the temperature of the cleaning liquid, lower the temperature of the electrolytic solution, and to minimize energy loss, the liquid fed from the cleaning device to the electrolytic reaction device and the return liquid from the electrolytic reaction device to the cleaning device It is preferable to exchange heat with a heat exchanger.

  In the cleaning apparatus, it is possible to perform cleaning by storing the cleaning liquid in the cleaning tank and immersing the material to be cleaned, but applying the cleaning liquid droplets to the material to be cleaned for effective cleaning. It can be performed. The formation of the droplets can be performed by a droplet jet forming apparatus that forms a jet of droplets of the cleaning liquid by mixing the cleaning liquid and gas. As the gas, for example, air, nitrogen, inert gas, or the like can be used. The specific configuration of the droplet jet forming device is not limited to a specific one, and a known one can be used. According to the cleaning with the droplets, a required amount of persulfuric acid solution can be reduced, and re-adhesion of the peeled resist or the like can be prevented.

  In addition, the cleaning apparatus includes a cleaning material holding unit that holds the cleaning material that receives the ejection of the droplets, and the posture and position of the cleaning material are adjusted so that the droplets can be effectively received. Determine. The specific configuration is not limited to a specific configuration, and can be configured by, for example, a clamp or an installation base. The holding means may change the posture and position of the material to be cleaned while receiving the ejection of droplets, or may change the droplet ejection position and direction of the droplet jet forming apparatus. In addition, both may change the position of each other.

  It is desirable that the solution fed to the electrolytic reaction apparatus is stored in a solution storage tank provided on the downstream side of the heat exchanger and gradually supplied to the electrolytic reaction apparatus. As a result, the temperature of the solution stored in the solution storage tank is lowered by heat exchange by the heat exchanger, and the self-decomposition of persulfate ions is suppressed to reduce the burden on the electrolytic reaction apparatus. In addition, it is possible to proceed with the decomposition of the resist melt and the like removed and removed by the cleaning device. In addition, the organic substance is contained in the solution sent from the cleaning device to the electrolytic reaction device due to dissolution of the resist, and the TOC can be measured by a TOC measuring device. The measurement result is a measure of the persulfuric acid concentration required for decomposition. Therefore, it can utilize for the condition setting of the electrolytic reaction apparatus mentioned later. For example, the TOC measuring device can be provided in the solution storage tank, and the solution stored in the storage tank can be used as a measurement target.

  In the electrolytic reaction apparatus, a high-concentration sulfuric acid solution is electrolyzed to produce persulfuric acid that enhances the cleaning effect. In the electrolytic reaction apparatus, as described above, the persulfuric acid generation efficiency is higher as the solution temperature is lower. Moreover, 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. The persulfuric acid solution regenerated by the electrolytic reaction device can be temporarily stored in the solution storage tank, mixed with the solution sent from the cleaning device, and then sent to the cleaning device. Thus, a persulfuric acid solution having a stabilized persulfuric acid concentration can be used as the cleaning liquid.

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 an anode, there is a problem that persulfate ions cannot be efficiently produced and platinum is eluted. On the other hand, when a conductive diamond electrode is used for at least the anode, there is an advantage that it is chemically stable and does not elute impurities in the concentrated sulfuric acid solution. The production of persulfuric acid from sulfuric acid by a conductive diamond electrode has been reported under conditions of 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)). The conductive diamond electrode is a semiconductor material such as a silicon wafer used as a substrate, and after synthesizing a conductive diamond thin film on the wafer surface, the wafer is dissolved or synthesized in a plate shape under the condition that the substrate is not used. Mention may be made of self-standing conductive polycrystalline diamond. 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, the electrolytic reaction apparatus is preferably a self-standing type conductive diamond electrode in which the substrate is removed after being deposited on the substrate. The conductive diamond thin film is one obtained by doping boron or nitrogen during synthesis of the diamond thin film to impart conductivity, and usually boron doped one. 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. . 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.
The electrolytic treatment in this electrolytic reaction apparatus is carried out by setting the current density on the surface of the conductive diamond electrode to 10 to 100,000 A / m ² , the sulfuric acid solution in the direction parallel to the diamond electrode surface, and the liquid flow rate of 10 to 10,000 m / m ^2. It is desirable to perform the contact treatment with h.

In electrolysis, the rate of increase in the total organic carbon concentration (TOC) of the solution by washing is obtained using the measurement results of the TOC measuring device described above, and (persulfuric acid production rate [g / l / hr] ) / ( Total organic carbon concentration (TOC) increase rate [g / l / hr] of the solution fed from the cleaning device to the electrolytic reaction device ) satisfies 10 to 500, and the current density and liquid passage It is desirable to determine the electrolytic conditions of speed and solution temperature. When the above value is less than 10, persulfuric acid is insufficient at the time of washing. On the other hand, when the above value exceeds 500, the generation of persulfuric acid becomes excessive and wasteful, and the electrode is also consumed quickly. Therefore, the above range is desirable.

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 present invention, a single-wafer cleaning apparatus that cleans an electronic material substrate by using a persulfuric acid solution heated to 100 ° C. or higher as a cleaning liquid and removes the resist on the substrate, and an electrolytic reaction To generate a persulfate ion from a sulfate ion contained in a solution having a sulfuric acid concentration within the range of 8M to 18M and a temperature within the range of 40 ° C to 90 ° C to regenerate the persulfuric acid solution Since the apparatus and the circulation line in which the solution and the electrolysis are circulated between the cleaning apparatus and the electrolytic reaction apparatus and a common solution storage tank is interposed between the feeding side and the return side , A persulfuric acid solution for repeatedly using the sulfuric acid solution and enhancing the peeling effect can be regenerated on-site by an electrolytic reactor and used for cleaning. Since the electrolyzed cleaning solution contains a large amount of persulfuric acid having a high cleaning effect, the substrate cleaning effect is higher than that of SPM. In addition, since the material to be cleaned is cleaned one by one by a single wafer type, the cleaning effect can be enhanced.

Below, one Embodiment of this invention is described based on FIG.
The sulfuric acid recycling type single wafer cleaning system of the present invention includes a cleaning apparatus including a cleaning tank 1, an electrolytic reaction apparatus including electrolytic reaction tanks 20 and 25, and a circulation line including return pipes 10a and 10b and feed pipes 11a and 11b. Is the main component.
In the cleaning device, a liquid spray nozzle 2 is provided as a droplet jet forming device, and a tip side ejection portion of the liquid spray nozzle 2 is located in the cleaning tank 1. Connected to the liquid spray nozzle 2 are a return pipe 10b of a circulation line for circulating a persulfuric acid solution to and from an electrolytic reaction apparatus to be described later, and an N ₂ gas supply pipe 3. The liquid spray nozzle 2 mixes the persulfuric acid solution supplied from the return pipe 10b with the high-pressure N ₂ gas supplied from the N ₂ gas supply pipe 3, and directs the droplets of the persulfuric acid solution downward. It is configured to erupt. The return pipe 10b is provided with a heating device 19 immediately before the connection portion of the liquid spray nozzle 2, and the persulfuric acid solution supplied to the liquid spray nozzle 2 is preferably heated to 100 to 150 ° C. .
In the cleaning tank 1, a substrate mounting table 4 is installed as a cleaning material holding means in the ejection direction of the liquid spray nozzle 2. A semiconductor substrate 30 as a material to be cleaned is placed on the substrate platform 4. It is desirable that the substrate mounting table 4 or the liquid spray nozzle 2 be relatively movable so that the liquid droplets uniformly hit the surface of the substrate 30.

  A feed pipe 11a of a circulation line is connected to the drainage section of the cleaning tank 1, and a feed pump 12 for feeding a persulfuric acid solution is interposed in the feed pipe 11a. A heat exchanger 13 that performs heat exchange is disposed between the return pipe 10b and the feed pipe 11a on the downstream side of the liquid feed pump 12, and is connected to the solution storage tank 14 on the downstream side. The solution storage tank 14 is connected to an ultrapure water supply line 15 for supplying ultrapure water, and further includes a TOC measuring device 28 for measuring the TOC of the stored solution. A feed pipe 11 b further extends from the solution storage tank 14 and is connected to a water inlet side of the electrolytic reaction tank 20 via a liquid feed pump 17.

  In the electrolytic reaction tank 20, an anode 21a and a cathode 21b are arranged, and further, bipolar electrodes 21c... 21c are arranged at a predetermined interval between the anode 21a and the cathode 21b. Note that the present invention is not limited to the bipolar type, and may include only an anode and a cathode as electrodes. A DC power source 22 is connected to the anode 21a and the cathode 21b, thereby enabling DC electrolysis in the electrolytic reaction tank 20.

The electrolytic reaction tank 20 is configured so that the solution passes between the electrodes. A connecting pipe 23 is connected to the water discharge side of the electrolytic reaction tank 20, and the other end is the water inlet side of the electrolytic reaction tank 25. It is connected to the.
The electrolytic reaction tank 25 has the same configuration as that of the electrolytic reaction tank 20, and an anode 26a and a cathode 26b are arranged. Further, a bipolar electrode 26c... Has a predetermined interval between the anode 26a and the cathode 26b. 26c is arranged. A DC power source 27 is connected to the anode 26a and the cathode 26b.

In this embodiment, the electrodes 21a, 21b, 21c, 26a, 26b, and 26c are constituted by diamond electrodes. 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. Alternatively, a self-stand type may be used by removing the substrate after forming the thin film.
A return pipe 10 a is connected to the water discharge side of the electrolytic reaction tank 25. That is, the electrolytic reaction apparatus is constituted by the electrolytic reaction tanks 20 and 25, the DC power sources 22 and 27, and the connecting pipe 23 connected in series.

  The return pipe 10a connected to the electrolytic reaction tank 25 is connected to the solution storage tank 14, and the return pipe 10b connected to the solution storage tank 14 is connected to the heat exchanger 13 via the liquid feed pump 18. Further, as described above, the liquid spray nozzle 2 is connected via the heating device 19 as described above.

Next, the operation of the sulfuric acid recycling type single wafer cleaning system configured as described above will be described.
The solution storage tank 14 contains sulfuric acid, which is mixed with ultrapure water at a predetermined volume ratio from the ultrapure water supply line 15 to obtain a sulfuric acid solution having a sulfuric acid concentration of 10 to 18M. This is sequentially fed to the electrolytic reaction tank 20 by the liquid feed pump 17. In the electrolytic reaction tank 20, when the anode 21a and the cathode 21b are energized by the DC power source 22, the bipolar electrodes 21c... 21c are polarized, and the anode and the cathode appear at predetermined intervals. The solution sent to the electrolytic reaction tank 20 is passed between these electrodes. At this time, it is desirable to set the output of the liquid feed pump 17 so that the liquid flow rate is 1 to 10,000 m / hr. In the above energization, it is desirable to energization control such that the current density at the diamond electrode surface is 10~100,000A / ^{m 2.}

  When the solution is energized in the electrolytic reaction tank 20, the sulfate ions in the solution undergo an oxidation reaction to produce persulfate ions, thereby obtaining a high concentration persulfate solution. This persulfuric acid solution is further sent from the connecting pipe 23 to the electrolytic reaction tank 25 and is energized by the DC power source 27 as in the electrolytic reaction tank 20 to generate persulfate ions. The persulfuric acid solution 16 having a high concentration in this way is temporarily stored in the solution storage tank 14 through the return pipe 10a. The persulfuric acid solution 16 stored in the solution storage tank 14 is fed to the cleaning tank 1 side by the liquid feed pump 18 through the return pipe 10b. The persulfuric acid solution to be fed passes through the heat exchanger 13, where the heat is exchanged with the solution in the feeding tube 11a fed from the washing tank 1 toward the solution storage tank 14, and the temperature rises. This persulfuric acid solution is further fed to the washing tank 1 side, heated to 100 to 150 ° C. by the heating device 19, and supplied to the liquid spray nozzle 2.

In the cleaning tank 1, the heated persulfuric acid solution and the N ₂ gas are mixed in the liquid spray nozzle 2, and high-temperature persulfuric acid droplets are ejected for a certain period of time.
A substrate 30 is placed on the substrate mounting table 4. The substrate 30 is rotated by the substrate mounting table 4, the surface of the substrate 30 is cleaned by the persulfuric acid droplets, and the resist and the like are peeled off and removed. . The ejected persulfuric acid solution is scattered and dropped after the substrate 30 is washed, and the dissolved resist and the like are discharged to the feed tube 11a. In the feed pipe 11a, the persulfuric acid solution is fed to the solution storage tank 14 side by the liquid feed pump 12. At this time, the heat exchanger 13 exchanges heat with the return pipe 10b to lower the temperature of the persulfuric acid solution. Further, the temperature is gradually lowered by natural cooling, and 10 ° C to 90 ° C suitable for the electrolytic reaction. The temperature is within the range of. Thereafter, it is temporarily stored in the solution storage tank 14. In addition, when it is desired to reliably lower the temperature, a cooling means for forcibly cooling the solution storage tank 14 by water cooling or air cooling may be provided. When the liquid is fed through the feed pipe 11a, the dissolved resist material peeled and removed in the cleaning tank 1 is decomposed. Moreover, in the solution storage tank 14, the temperature of the solution has fallen by the said heat exchange, and the self-decomposition is suppressed. Further, when the solution is temporarily stored in the solution storage tank 14, the decomposition of the resist melt proceeds, and the inflow of the resist melt into the electrolytic reaction apparatus is effectively prevented.

In the solution storage tank 14, TOC is generated as the resist and other contaminants are peeled and dissolved in the single wafer cleaning apparatus. The TOC is measured by the TOC measuring device 28, and the TOC increase rate can be calculated based on the temporal change of the measurement result.
Based on this TOC increase rate, in the electrolytic reaction tanks 20 and 25, (persulfuric acid production rate [g / l / hr]) / (TOC increase rate in cleaning liquid tank [g / l / hr]) is 10 to 500. The electrolysis conditions are set so as to satisfy. The electrolysis conditions can be set by adjusting the current density, the liquid flow rate, and the solution temperature.

The persulfate solution 16 accommodated in the solution storage tank 14 is then sent to the electrolytic reaction apparatus in the same manner as described above, and the persulfate ion concentration is reduced by self-decomposition to generate persulfate ions from the sulfate ions. Then, the persulfuric acid solution is regenerated and stored again in the solution storage tank 14, and then returned to the cleaning device and used as a cleaning liquid in the same manner as described above.
By cleaning semiconductor wafers using the sulfuric acid recycling type single wafer cleaning system, it is effective to regenerate the persulfuric acid solution by repeatedly using sulfuric acid solution without the need for hydrogen peroxide or ozone. Cleansing can be continued.

Examples using the sulfuric acid recycling type single wafer cleaning system of the above embodiment will be described below.
A high-concentration sulfuric acid solution (14.8M) prepared at a ratio of 98 liters of concentrated sulfuric acid 40 liters and ultrapure water 10 liters was stored in the solution storage tank 14. In the electrolytic reaction apparatus, two electrolytic reaction tanks 20 and 25 each incorporating 10 boron-doped conductive diamond electrodes having a diameter of 15 cm and a thickness of 0.5 mm were arranged in series. Effective anode area for electrolysis is 30dm ^2, and electrolysis by setting the current density 30A / dm ^2. At this time, in the electrolytic reaction apparatus, it was confirmed that the persulfuric acid production rate was 3 g / l / hr. The cleaning solution containing persulfuric acid from the solution storage tank was supplied to a single wafer cleaning apparatus at 150 ml / min. In the middle of this, it was heated to about 130 ° C. with a heating device and introduced into a two-fluid spray nozzle. A 5-inch silicon wafer with a resist held on the substrate mounting table is placed for 3 min. / Washed at a rate of about 1 sheet. The waste liquid was collected in the solution storage tank 14. This process was performed continuously for 3 hours, and 60 clean wafers could be obtained. During this time, no new chemical was added, and the TOC concentration of the cleaning liquid in the solution storage tank was below the detection limit.

(Comparative Example 1)
The single wafer cleaning apparatus of Example 1 was used, and the cleaning liquid was mixed with sulfuric acid: hydrogen peroxide solution 4: 1 and heated to 130 ° C. to the cleaning apparatus. A 5-inch silicon wafer with a resist is added for 3 min. / Washed at a rate of about 1 sheet. After 3 hours, 60 clean wafers could be obtained, but about 27 L of cleaning waste liquid was generated.

(Comparative Example 2)
Without electrolytic treatment using the same apparatus and processing conditions as in Example 1, a 5-inch silicon wafer with a resist was added for 3 min. / Washed at a rate of about 1 sheet. As a result of performing for 3 hours, clean wafers could be obtained up to the first 20 wafers, but the subsequent wafers could not be completely cleaned due to organic substances adhering to the surface. The cleaning liquid in the solution storage tank was gradually colored brown from the start of cleaning and the TOC concentration increased, and the TOC concentration after 3 hours became about 30 mg / l.

It is a figure which shows the sulfuric acid recycle type | mold sheet type washing system of one Embodiment of this invention.

Explanation of symbols

Feed 1 cleaning tank 2 liquid spray nozzle 3 N ₂ gas supply pipe 4 substrate mounting table 10a return pipe 10b return pipe 11a feed pipe 11b feed pipe 12 feeding pump 13 heat exchanger 14 solution storage tank 16 persulfate solution 17 liquid feed pump 18 Liquid pump 19 Heating device 20 Electrolytic reaction tank 21a Anode 21b Cathode 21c Bipolar electrode 22 DC power supply 23 Connecting pipe 25 Electrolytic reaction tank 26a Anode 26b Cathode 26c Bipolar electrode 27 DC power supply 30 Substrate

Claims (9)

Using a persulfuric acid solution heated to 100 ° C. or more as a cleaning liquid, a single-wafer type cleaning device that cleans the electronic material substrate and removes the resist on the substrate , and a sulfuric acid concentration in the range of 8M to 18M by electrolytic reaction. An electrolytic reaction device for generating persulfate ions from sulfate ions contained in a solution having a temperature within a range of 40 ° C. to 90 ° C. to regenerate the persulfuric acid solution, and the cleaning device and the electrolytic reaction device A sulfuric acid recycle type single wafer cleaning system comprising a circulation line in which a solution is circulated while performing the cleaning and the electrolysis between them, and a common solution storage tank is interposed between the feeding side and the return side . The sulfuric acid recycling type single wafer cleaning system according to claim 1, further comprising a heating device that sets the temperature of the cleaning liquid to 100 to 150 ° C. The sulfuric acid recycle type single wafer cleaning system according to claim 1 or 2, wherein at least an anode of an electrode used in the electrolytic reaction apparatus is a conductive diamond electrode . The electrolytic reaction apparatus has a (persulfuric acid production rate [g / l / hr]) / (total organic carbon concentration (TOC) increase rate [g / l / hr] of the solution fed from the cleaning apparatus to the electrolytic reaction apparatus. The sulfuric acid recycle type single wafer cleaning system according to any one of claims 1 to 3 , wherein electrolysis is performed so as to satisfy 10 to 500 . A heat exchanger that exchanges heat between the solution on the sending side and the solution on the return side of the circulation line, and that the solution storage tank is interposed on the side of the electrolytic reaction device than the heat exchanger. sulfuric acid recycle type single wafer cleaning system according to any one of claims 1 to 4, characterized. The sulfuric acid recycle according to any one of claims 1 to 5, wherein the single wafer cleaning device includes a droplet jet forming device that forms a jet of droplets of the cleaning liquid by mixing the cleaning liquid and gas. Mold single wafer cleaning system. The sulfuric acid recycle type single wafer cleaning according to any one of claims 1 to 6, wherein the single wafer cleaning apparatus includes a substrate holding means for holding a material to be cleaned that receives a droplet jet of the cleaning liquid. system. The sulfuric acid recycling according to any one of claims 1 to 7, wherein the electronic material substrate is used for the cleaning without undergoing a pretreatment step in which the resist is oxidized and incinerated in advance. Mold single wafer cleaning system. The electronic material substrate is cleaned by a single wafer method using a persulfuric acid solution of 100 ° C. or higher as a cleaning solution to remove the resist on the substrate, and has an sulfuric acid concentration within a range of 8M to 18M by an electrolytic reaction, and the temperature is A persulfate ion is generated from a sulfate ion contained in a solution within a range of 40 ° C. to 90 ° C. to regenerate the persulfate solution, and the solution in the washing and the solution in the electrolytic reaction are subjected to the washing and the electrolysis. Meanwhile, a sulfuric acid recycle type single wafer cleaning method, wherein the feed side and the return side are circulated through a common liquid storage.

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