JP2007059603A - Sulfuric acid recycling type cleaning system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve throughput while obtaining a cleaning system which can continue cleaning, in a cleaning system using persulfate ions. <P>SOLUTION: The sulfuric acid recycling type cleaning system comprises: a single wafer process cleaning equipment 1 for cleaning a material 30 to be cleaned by using a persulfuric acid solution as a cleaning fluid; electrolysis reaction tubs 20 and 25 for reproducing the persulfuric acid solution by generating persulfate ions from sulfuric acid ions contained in the solution by an electrolysis reaction; circulation lines 10a, 10b, 11a and 11b for circulating the persulfuric acid solution between a cleaning tub 1 and the electrolysis reaction tubs 20 and 25 which generate; and an ultraviolet-ray irradiation means 5 for irradiating ultraviolet-ray to the material 30 to be cleaned. Since a sulfuric acid solution is repeatedly used, the persulfuric acid solution can be reused in an on-site way for cleaning by utilizing an electrolysis reaction device. When cleaning, the generation of the sulfuric acid radicals is promoted while being irradiated by ultraviolet-ray to the cleaning solution, resulting in the improvement in the cleaning effect. It becomes possible to shorten working hours and to improve the throughput. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 recycling type cleaning system that regenerates and uses for cleaning.

In technologies for cleaning electronic material substrates such as silicon wafers, liquid crystal glass substrates, and photomask substrates in the VLSI manufacturing process, the resist stripping and cleaning process is usually a mixed solution of concentrated sulfuric acid and hydrogen peroxide (SPM) or A solution (SOM) in which ozone gas is blown into concentrated sulfuric acid is often used. It has been found that the cleaning effect by SPM or SOM lies in the high oxidation resolution of persulfuric acid produced by hydrogen peroxide oxidizing sulfuric acid.
In SPM, hydrogen peroxide solution needs to be replenished to compensate for the amount of decomposition and decrease of persulfuric acid. Since the concentrated sulfuric acid solution is diluted with water in hydrogen peroxide water each time, 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. Therefore, there is a problem that a large amount of chemicals must be stored.
On the other hand, the concentrated sulfuric acid solution is not diluted with one SOM and the liquid renewal cycle can be made longer than that of SPM. However, the production efficiency of persulfuric acid by ozone is low, and the cleaning effect is slightly inferior to SPM. In these methods, the concentration of persulfuric acid produced has a limit, which has led to the limit of the cleaning effect.
In the SPM and SOM processes described above, as a pretreatment process, a dry etching or ashing process is used to oxidize and ash the organic resist in advance. There is a problem that becomes expensive.

  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 prior arts relating to the single wafer cleaning apparatus, those shown in Patent Documents 1 and 2 have been proposed. Patent Document 1 discloses a cleaning device including a stage that rotates while holding a single substrate substantially horizontally, and a hopper for supplying a cleaning liquid to the surface of the substrate held on the stage. 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. 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. In addition, the single-wafer cleaning is effective, but the objects to be cleaned must be processed one by one. Therefore, the throughput of the apparatus is not good, and the cleaning speed is increased to improve the throughput. Processing is required.

  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. Furthermore, an object of the present invention is to provide a sulfuric acid recycle type cleaning system capable of increasing the cleaning speed and improving the processing efficiency.

  The inventors of the present invention diligently invented a technique for overcoming the problems of the prior art described above and continuously supplying a persulfuric acid solution having a high cleaning effect in a continuous and large amount. According to the present invention, not only as an alternative cleaning method of the SPM method or SOM method, but also a dry process such as ashing, which is a pre-process of the SPM method or SOM method, can be omitted.

  That is, in the sulfuric acid recycle type cleaning system of the present invention, the invention according to claim 1 is a cleaning device for cleaning a material to be cleaned using a persulfuric acid solution as a cleaning liquid, a substrate heating unit for heating the material to be cleaned, An electrolytic reaction apparatus for producing a persulfuric acid solution by electrolyzing the cleaning liquid discharged from the cleaning apparatus and generating persulfate ions from sulfate ions contained in the cleaning liquid, and circulating the solution between the cleaning apparatus and the electrolytic reaction apparatus And a circulation line to be provided.

  The sulfuric acid recycling type cleaning system according to claim 2 is characterized in that, in the invention according to claim 1, the heating means heats the material to be cleaned in a range of 70 ° C to 250 ° C.

  According to a third aspect of the present invention, there is provided a cleaning apparatus for cleaning a material to be cleaned using a persulfuric acid solution as a cleaning liquid, an ultraviolet irradiation means for irradiating the cleaning liquid with ultraviolet light, and a cleaning liquid discharged from the cleaning apparatus. An electrolytic reaction device for producing a persulfuric acid solution by producing persulfate ions from sulfate ions contained in the cleaning liquid by electrolysis, and a circulation line for circulating the solution between the cleaning device and the electrolytic reaction device. It is characterized by that.

  The invention of a sulfuric acid recycling type cleaning system according to claim 4 is the invention according to any one of claims 1 to 3, wherein the cleaning device is a single wafer cleaning device.

  According to a fifth aspect of the present invention, there is provided a sulfuric acid recycling type cleaning system according to the fourth aspect, wherein the single wafer cleaning device is a droplet jet that forms a jet of droplets of the cleaning liquid by mixing the cleaning liquid with gas. A forming apparatus is provided.

  The invention of the sulfuric acid recycling type cleaning system according to claim 6 is characterized in that, in the invention according to any one of claims 1 to 5, the sulfuric acid concentration of the cleaning liquid is in the range of 8M to 18M.

  A seventh aspect of the invention of the sulfuric acid recycling type cleaning system includes the heating apparatus according to any one of the first to sixth aspects, wherein the temperature of the cleaning liquid used in the cleaning apparatus is 100 to 175 ° C. And

  The invention of the sulfuric acid recycle type cleaning system according to claim 8 is the invention according to any one of claims 1 to 7, wherein the temperature of the solution electrolyzed in the electrolytic reaction device is in the range of 10 ° C to 90 ° C. It is characterized by that.

  The invention of the sulfuric acid recycling type cleaning system according to claim 9 is the invention according to any one of claims 1 to 8, characterized in that at least the anode of the electrode used in the electrolytic reaction device is a conductive diamond electrode. And

  The invention of the sulfuric acid recycling type cleaning system according to claim 10 is the invention according to any one of claims 1 to 9, wherein heat is exchanged between the solution on the feed side and the solution on the return side of the circulation line. It is characterized by having an exchanger.

  According to the present invention, persulfate ions in the cleaning liquid self-decompose and emit oxidizing power. In the material to be cleaned that is in contact with the cleaning liquid, contaminants are effectively peeled and removed by the action of sulfuric acid and persulfate ions, and the contaminants that have moved into the cleaning liquid are decomposed by the action of persulfate ions. And in a washing | cleaning liquid, a persulfate ion density | concentration falls gradually, when the persulfate ion in a solution self-decomposes. This persulfuric acid solution is sent to the electrolytic reactor through a circulation line. In an electrolytic reaction apparatus, an anode and a cathode are immersed in a solution containing sulfate ions, and a current is passed between the electrodes to perform electrolysis, whereby sulfate ions are oxidized to produce persulfate ions, and a persulfate ion concentration is sufficiently high. Regenerated to sulfuric acid 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 high-concentration persulfate ions 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.

  In addition, as the temperature of persulfate ions increases, the self-decomposition rate increases and a high peeling cleaning action is obtained. 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, it is desirable that the cleaning liquid is 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 175 ° C. Below this temperature range, the effect of stripping and cleaning with persulfuric acid decreases. On the other hand, if the temperature exceeds 175 ° C., the self-decomposition rate of persulfuric acid becomes extremely high and the resist cannot be sufficiently oxidized, so that the appropriate temperature of the cleaning liquid is within the above range.

  As described above, the cleaning effect on the object to be cleaned is greatly affected by the temperature of the cleaning liquid. In the batch system, (1) the amount of concentrated sulfuric acid solution with respect to the wafer is large, (2) the wafer immersion time is relatively long as 5 to 10 minutes, and (3) the heater is in the cleaning bath, it is at room temperature. Even if the wafer is processed, an appropriate wafer temperature is reached in the latter half of the cleaning. On the other hand, in the single wafer type, (1) the amount of concentrated sulfuric acid solution with respect to the wafer is small, (2) the wafer immersion time is as short as 2 to 5 minutes, and (3) the cleaning unit does not have a heater. As a result, the wafer temperature often does not reach the optimum temperature during cleaning. Therefore, according to one aspect of the present invention, when cleaning a material to be cleaned by spraying a cleaning liquid or the like, when the temperature of the material to be cleaned is low, it is possible to increase the cleaning efficiency by heating the material to be cleaned. . In the present invention, the material to be cleaned is preferably heated to 70 ° C. to 250 ° C., more preferably 100 ° C. to 180 ° C. to enable highly efficient cleaning.

  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 the single wafer type, cleaning can be performed effectively with a small amount of cleaning liquid, but since the processing is performed one by one, the throughput is not sufficient as described above.
Therefore, in one embodiment of the present invention, an ultraviolet irradiation means such as a low-pressure mercury lamp is provided, and the surface of the material to be cleaned is irradiated with ultraviolet light in the presence of a cleaning liquid to further improve the cleaning effect and improve the throughput. I am trying. Persulfuric acid present in the cleaning solution generates sulfate radicals during decomposition, but it is known that the decomposition rate is improved by absorbing ultraviolet light (for example, SW Kuo, J. Environ. Sci. Health Part A). , Vol. A37, No. 8, pp 1581-1591, 2002). Even in the cleaning apparatus, the decomposition rate of persulfuric acid increases, and organic substances can be decomposed and removed more efficiently on the surface of the object to be cleaned.

  The high-concentration sulfuric acid solution used in the cleaning device and sent to the electrolytic reaction device has a high temperature of about 100 ° C. Therefore, it is desirable that the high-concentration sulfuric acid solution is once stored in the solution storage tank and gradually supplied to the electrolytic reaction device. . As a result, the temperature of the solution stored in the solution storage tank gradually decreases, and the self-decomposition of persulfate ions is suppressed to reduce the burden on the electrolytic reaction device, and during the temporary storage, the cleaning device removes and removes it with persulfate. It is possible to proceed with the decomposition of the dissolved resist. 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 concentration of persulfuric acid 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 addition, the solution in the storage tank is at a high temperature, and it is not preferable to send the solution to the electrolytic reaction device as it is. For example, after the heat is exchanged with the solution returned from the electrolytic reaction device to the cleaning device, the temperature is lowered. It is desirable to supply the reactor. Thereby, energy loss can be reduced as much as possible. The solution temperature returned from the electrolytic reaction apparatus to the washing apparatus becomes several tens of degrees Celsius higher than the electrolysis temperature of 40 degrees Celsius due to heat exchange, but the residence time in the pipe is short, and less persulfate ions disappear. It is desirable that the heat exchanger has a flow path made of quartz or Teflon (trademark).

  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 generating persulfate ions 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.

  In the electrolytic reaction apparatus, a high-concentration sulfuric acid solution is electrolyzed to generate persulfate ions that enhance the cleaning effect. In the electrolytic reaction apparatus, as described above, the lower the solution temperature, the higher the production efficiency of persulfate ions. Moreover, the production efficiency of persulfate ions in the electrolytic reaction apparatus is greatly influenced by the sulfuric acid concentration. Specifically, persulfate ion 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 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. Generation of persulfate ions 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. Comninellis 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 performed 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 1 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 (persulfate ion production rate [g / l / hr ]) / (TOC increase rate [g / l / hr]) preferably satisfies the electrolysis conditions of the current density, the liquid flow rate, and the solution temperature so as to satisfy 10 to 500. When the above numerical value is less than 10, persulfuric acid is insufficient at the time of washing. On the other hand, when the above numerical value exceeds 500, the generation of persulfate ions 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 one aspect of the present invention, a cleaning apparatus that cleans a material to be cleaned using a persulfuric acid solution as a cleaning liquid, a substrate heating unit that heats the material to be cleaned, and a discharge from the cleaning apparatus. An electrolytic reaction device for producing a persulfuric acid solution by electrolyzing the cleaning solution to generate persulfate ions from sulfate ions contained in the cleaning solution; and a circulation line for circulating the solution between the cleaning device and the electrolytic reaction device. Therefore, a persulfuric acid solution for repeatedly using the sulfuric acid solution and enhancing the peeling effect can be regenerated on-site by an electrolytic reaction device and used for cleaning. Since the electrolyzed cleaning solution contains a large amount of persulfate ions having a high cleaning effect, the substrate cleaning effect is higher than that of SPM. Further, when the material to be cleaned is at a low temperature such as room temperature when it is cleaned by a single wafer type cleaning device, it is possible to obtain a good cleaning effect and improve the throughput.

  Furthermore, according to another aspect of the present invention, a cleaning apparatus that cleans a material to be cleaned using a persulfuric acid solution as a cleaning liquid, an ultraviolet irradiation means that irradiates the cleaning liquid with ultraviolet light, and a cleaning liquid discharged from the cleaning apparatus is electrolyzed. An electrolytic reaction device that produces persulfate ions from sulfate ions contained in the cleaning solution to produce a persulfuric acid solution, and a circulation line that circulates the solution between the cleaning device and the electrolytic reaction device. Similarly to the above, a sulfuric acid solution can be repeatedly used and a persulfuric acid solution for enhancing the peeling effect can be regenerated on-site by an electrolytic reactor and used for cleaning. Moreover, by irradiating the cleaning liquid with ultraviolet rays, the decomposition of persulfate ions is promoted, the cleaning effect is enhanced, and the throughput can be improved.

(Embodiment 1)
Below, one Embodiment of this invention is described based on FIG.
The sulfuric acid recycling type cleaning system of the present invention includes a single wafer cleaning device including a cleaning tank 1, an electrolytic reaction device 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 single wafer 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. .

  Further, a substrate holder 4 is installed in the cleaning tank 1 in the ejection direction of the liquid spray nozzle 2. The substrate holder 4 holds (places, etc.) a semiconductor substrate 30 that is a material to be cleaned. It is desirable that the substrate holder 4 or the liquid spray nozzle 2 be relatively movable so that the liquid droplets uniformly hit the surface of the substrate 30. Further, in the cleaning tank 1, ultraviolet irradiation means 5 including an ultraviolet light irradiation device such as a low-pressure mercury lamp that irradiates ultraviolet light toward the substrate 30 held by the substrate holder 4 is disposed. Above the irradiating means 5, there is provided a reflecting plate 6 that reflects ultraviolet light toward the substrate 30 side.

And the feed line 11a of the circulation line is connected to the drainage part of the said washing tank 1, The feed pump 12 for feeding a persulfuric acid solution is interposed in this 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. An ultrapure water supply line 15 for supplying ultrapure water is connected to the solution storage tank 14. Moreover, you may provide the TOC measuring device which measures TOC of the solution accommodated if desired. A feed pipe 11 b extends further from the outlet side of the solution storage tank 14, and is connected to the inlet side of the electrolytic reaction tank 20 via a liquid feed pump 17.
The return pipes 10a and 10b, the feed pipes 11a and 11b, and the flow path of the heat exchanger 13 are preferably made of quartz or Teflon that is durable against a persulfuric acid solution.

  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 outlet side of the electrolytic reaction tank 20, and the other end is the inlet side of the electrolytic reaction tank 25. It is connected to the.
In the electrolytic reaction tank 25, as in the electrolytic reaction tank 20, an anode 26a and a cathode 26b are arranged, and further, bipolar electrodes 26c... 26c are arranged at a predetermined interval between the anode 26a and the cathode 26b. . 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 outlet 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 10 a connected to the electrolytic reaction tank 25 is connected to the solution storage tank 14, and the return pipe 10 b connected to the solution storage tank 14 is further connected to the heat exchanger 13 via the liquid feed pump 18. And further connected to the liquid spray nozzle 2 via the heating device 19 as described above.

Next, the operation of the sulfuric acid recycling type cleaning system having the above configuration 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 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 tank 20, persulfate ions in the solution are generated by oxidation reaction, and a high concentration persulfate solution is obtained. 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 in the same manner as the electrolytic reaction tank 20 to further 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 175 ° 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. At this time, the ultraviolet irradiation means 5 is operated to irradiate ultraviolet light. The ultraviolet light is directly irradiated toward the substrate holder 4, and a part of the ultraviolet light is reflected by the reflecting plate 6 and is also irradiated toward the substrate holder 4.
A substrate 30 is held on the substrate holder 4, the surface of the substrate 30 is cleaned by the persulfuric acid droplets, and the resist and the like are peeled and removed by the action of sulfuric acid and persulfate ions. At this time, the substrate 30 is irradiated with ultraviolet light from the ultraviolet irradiation means 5, and when the persulfuric acid droplets ejected from the liquid spray nozzle 2 reach the surface of the substrate 30, the substrate 30 is irradiated with ultraviolet light and excessively irradiated. The production of sulfate ions is promoted and the cleaning effect is enhanced. As a result, the action of peeling and removing the resist and the like can be improved, and the working time for cleaning the substrate 30 can be shortened.

  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 near the range. 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 resist dissolved material peeled and removed in the cleaning tank 1 is decomposed by the action of persulfate ions. 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. This TOC can be measured by a TOC measuring device, and the TOC increase rate can be calculated based on the temporal change of the measurement result.
Based on the TOC increase rate, in the electrolytic reaction tanks 20 and 25, (persulfate ion generation rate [g / l / hr]) / (TOC increase rate in cleaning solution tank [g / l / hr]) is 10 to 500. It is desirable to set the electrolysis conditions so as to satisfy the above. The electrolysis conditions can be set by adjusting the current density, the liquid flow rate, and the solution temperature.

Thereafter, the persulfuric acid solution 16 accommodated in the solution storage tank 14 is sent to the electrolytic reaction apparatus 20 in the same manner as described above. In the electrolysis reactors 20 and 25, a persulfate ion concentration is reduced by autolysis to generate persulfate ions from the sulfate ions to regenerate the persulfate solution. The regenerated persulfuric acid solution is again stored 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. Further, the improvement of the cleaning effect can shorten the cleaning time and improve the throughput.

(Embodiment 2)
Next, another embodiment of the present invention will be described with reference to FIG. In addition, about the structure similar to the said Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted or simplified.
The sulfuric acid recycling type cleaning system of this embodiment includes a single wafer cleaning device including a cleaning tank 1a, an electrolytic reaction device including electrolytic reaction tanks 20 and 25, and a circulation line including a return pipe 10 and feed pipes 11a and 11b. The main structure.

In the single wafer cleaning apparatus, a liquid spray nozzle 2 is provided, and a return pipe 10 of a circulation line and an N ₂ gas supply pipe 3 are connected to the liquid spray nozzle 2. Further, in the cleaning tank 1, a substrate holder 4 is installed in the ejection direction of the liquid spray nozzle 2, and a substrate heating means 7 including a heater for heating the substrate 30 held by the substrate holder 4 is provided. Is provided.

  The feed pipe 11a of the circulation line connected to the drainage part of the washing tank 1 is connected to the solution storage tank 14, and the feed pipe 11b connected to the outlet side of the solution storage tank 14 includes a heat exchanger 13 and persulfuric acid. A liquid feed pump 17 for feeding the solution is interposed. The feed pipe 11 b is connected to the inlet side of the electrolytic reaction tank 20 on the downstream side of the liquid feed pump 17.

  The electrolytic reaction tank 20 and the electrolytic reaction tank 25 are connected in series via a connecting pipe 23, and the return pipe 10 is connected to the outlet side of the electrolytic reaction tank 25. The return pipe 10 connected to the electrolytic reaction tank 25 is connected to the liquid spray nozzle 2 via the heat exchanger 13.

  In the sulfuric acid recycling type cleaning system having the above-described configuration, sulfuric acid is accommodated in the solution storage tank 14 as in the above embodiment, and ultrapure water is mixed into the solution storage tank 14 at a predetermined volume ratio from the ultrapure water supply line 15. A sulfuric acid solution having a sulfuric acid concentration of 10 to 18M is used. This is sequentially sent to the electrolytic reaction tank 20 by the liquid feed pump 17, and the persulfuric acid is regenerated in the electrolytic reaction tanks 20 and 25. The regenerated persulfuric acid solution is fed through the return pipe 10 to the washing tank 1a side by the liquid feeding pump 18. 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 11b fed from the solution storage tank 14 toward the electrolytic reaction tank 20, and the temperature rises. . The sulfuric acid solution passing through the return pipe 10 is fed to the washing tank 1 a side and supplied to the liquid spray nozzle 2.

In the washing tank 1a, persulfuric acid droplets are ejected from the liquid spray nozzle 2 for a certain period of time. At this time, the substrate heating means 7 is operated to heat the substrate 30 held by the substrate holder 4 to 70 ° C. to 250 ° C., more preferably 100 ° C. to 180 ° C. The persulfuric acid droplets ejected from the liquid spray nozzle 2 are brought into contact with the high-temperature substrate 30 to increase the temperature, preferably 100 to 175 ° C. In addition, in order to ensure that the temperature of the cleaning liquid is an appropriate temperature, it is possible to preheat it with a heating device or the like as in the above embodiment.
The surface of the substrate 30 is cleaned by the persulfuric acid droplets having the appropriate temperature, and the resist and the like are peeled and removed by the action of sulfuric acid and persulfate ions. As a result, the action of peeling and removing the resist and the like is improved, and the working time for cleaning the substrate 30 can be shortened.

  The ejected persulfuric acid solution is fed to the solution storage tank 14 side as in the above embodiment. Thereafter, through the heat exchanger 13, heat is exchanged with the return pipe 10, the temperature of the persulfuric acid solution is lowered, and the temperature is in the range of 10 ° C to 90 ° C suitable for the electrolytic reaction. Thereafter, the persulfuric acid solution is sent to the electrolysis reactors 20 and 25 in the same manner as described above, and the persulfate ions are generated from the sulfate ions by electrolyzing the solution having a reduced persulfate ion concentration by autolysis. Regenerate the solution. Then, it is accommodated in the solution storage tank 14 again, and then returned to the cleaning device and used as a cleaning liquid in the same manner as described above. Also in this embodiment, an object to be cleaned such as a silicon wafer can be efficiently cleaned, and the throughput can be improved.

As mentioned above, although this invention was demonstrated based on the said embodiment, this invention is not limited to the content of these embodiment, In the range which does not deviate from the scope of the present invention, a change is possible.
In the above embodiment, the cleaning apparatus has been described as having either one of the ultraviolet irradiation means and the heating means, but the present invention naturally includes both the ultraviolet irradiation means and the heating means. Also good.

Hereinafter, examples using the sulfuric acid recycling type cleaning system of the first embodiment will be described.
A high-concentration sulfuric acid solution prepared at a ratio of 40 liters of 97% concentrated sulfuric acid and 10 liters of ultrapure water was stored in the solution storage tank. 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 persulfate ion production rate was 3 g / l / hr. A cleaning solution containing persulfate ions from a solution storage tank was placed in 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. While irradiating ultraviolet light from a low-pressure mercury lamp onto a 5-inch silicon wafer with a resist held by a substrate holder, it is 2 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 90 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 surface to be cleaned is not irradiated with ultraviolet light by the single wafer cleaning apparatus of Example 1, and a 5-inch silicon wafer with a resist is applied for 2 min. / Washed at a rate of about 1 sheet. The cleaning solution was a sulfuric acid / hydrogen peroxide solution mixed at a ratio of 4: 1 and heated to 130 ° C. After 3 hours, 82 clean wafers could be obtained, but the resist remained partially on the 8 wafers. Therefore, it is necessary to reduce the processing speed in the processing without irradiation with ultraviolet rays.

(Example 2)
Next, an example using the sulfuric acid recycling type cleaning system of Embodiment 2 will be described.
In the electrolytic reaction apparatus, 10 conductive diamond electrodes doped with boron on a Si substrate having a diameter of 15 cm and a thickness of 1 mm were incorporated. Two electrolytic cells were arranged in series. Effective anode area for electrolysis is 15Dm ^2, by setting the current density 30A / dm ^2, and electrolysis 97% concentrated sulfuric acid 40 liters, a mixed solution of ultrapure 8 liters of water at 40 ° C.. In the cleaning tank, a 5-inch silicon wafer with a resist not subjected to ashing was placed on a substrate holder and heated to 130 ° C. A sulfuric acid solution containing persulfuric acid was added at 1 l / min. Circulated at a moderate flow rate and introduced into the spray nozzle. A droplet of sulfuric acid solution containing persulfuric acid was formed with nitrogen gas, and 3 min. The wafer with resist was cleaned at a rate of about 1 / sheet. Such wafer cleaning was continued for 8 hours (160 wafers were cleaned), but the resist stripping effect of the high-concentration sulfuric acid solution was good, and the TOC concentration was also below the detection limit. Therefore, although it continued for 32 hours (the number of cleaning wafers was 640, the total number of processed wafers was 800), the resist stripping effect of the high-concentration sulfuric acid solution was good, and the TOC concentration was also below the detection limit.

(Comparative Example 2-1)
Using the cleaning apparatus of Example 2, 48 liters of a 5: 1 mixed sulfuric acid: hydrogen peroxide solution was circulated, and droplets were formed by a spray nozzle. A wafer with a resist that has not been subjected to an ashing process for 3 min. Washed at a rate of / sheet. When cleaning was continued while adding hydrogen peroxide in the middle, 80 clean wafers could be obtained after 4 hours, but 60 liters of waste liquid was generated, and the solution had to be replaced.

(Comparative Example 2-2)
Using the same apparatus and processing conditions as in Example 2, the wafer heating temperature was set at 80 ° C., and a resist-coated wafer that was not subjected to ashing was processed for 3 min. / Washed at a rate of about 1 sheet. Organic substances remained on the wafer surface and could not be completely cleaned.

It is a figure which shows the sulfuric acid recycle type single wafer cleaning system of one Embodiment of this invention. Similarly, it is a figure which shows the sulfuric acid recycle type single wafer cleaning system of other one embodiment.

Explanation of symbols

1 cleaning tank 1a washing tank 2 liquid spray nozzle 3 N ₂ gas supply pipe 4 substrate holder 5 the ultraviolet light irradiation means 6 reflector 7 substrate heating means 10 return pipe 10a return pipe 10b return pipe 11a feed pipe 11b feed pipe 12 feeding pump 13 Heat Exchanger 14 Solution Storage Tank 15 Ultrapure Water Supply Line 16 Persulfuric Acid Solution 17 Liquid 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 (10)

  A cleaning device that cleans a material to be cleaned using a persulfuric acid solution as a cleaning solution, a substrate heating means that heats the material to be cleaned, and a persulfate ion from sulfate ions contained in the cleaning solution by electrolyzing the cleaning solution discharged from the cleaning device A sulfuric acid recycle type cleaning system comprising: an electrolytic reaction device that produces a persulfuric acid solution by generating a circulation line for circulating the solution between the cleaning device and the electrolytic reaction device.   2. The sulfuric acid recycling type cleaning system according to claim 1, wherein the heating means heats the material to be cleaned in a range of 70 to 250 [deg.] C.   A cleaning device for cleaning a material to be cleaned using a persulfuric acid solution as a cleaning liquid, an ultraviolet irradiation means for irradiating the cleaning liquid with ultraviolet light, and a persulfate ion from sulfate ions contained in the cleaning liquid by electrolyzing the cleaning liquid discharged from the cleaning apparatus A sulfuric acid recycle type cleaning system comprising: an electrolytic reaction device that produces a persulfuric acid solution by generating a circulation line for circulating the solution between the cleaning device and the electrolytic reaction device.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 3, wherein the cleaning device is a single wafer cleaning device.   5. The sulfuric acid recycle type cleaning system according to claim 4, wherein the single wafer cleaning apparatus includes a droplet jet forming device that forms a jet of droplets of the cleaning liquid by mixing the cleaning liquid with a gas.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 5, wherein the sulfuric acid concentration of the cleaning liquid is within a range of 8M to 18M.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 6, further comprising a heating device that sets a temperature of a cleaning liquid used in the cleaning device to 100 to 175 ° C.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 7, wherein the temperature of the solution electrolyzed in the electrolytic reaction apparatus is in the range of 10 ° C to 90 ° C.   9. The sulfuric acid recycle type cleaning system according to claim 1, wherein at least an anode of an electrode used in the electrolytic reaction apparatus is a conductive diamond electrode.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 9, further comprising a heat exchanger that exchanges heat between the solution on the feed side and the solution on the return side of the circulation line. .

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