JP4407529B2 - Sulfuric acid recycling cleaning system - Google Patents

Description

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

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

JP 2001-192874 A Special table 2003-511555 gazette

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

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

  The present invention has been made against the background of the above circumstances, and the amount of sulfuric acid used can be recycled by efficiently generating persulfate ions from an aqueous solution of sulfuric acid by electrochemical action while repeatedly using sulfuric acid. The purpose is to provide a sulfuric acid recycle type cleaning system that can significantly reduce

That is, the invention according to claim 1 of the sulfuric acid recycle type cleaning system of the present invention includes a cleaning apparatus for cleaning a semiconductor substrate using a heated persulfuric acid solution as a cleaning liquid, and an excess of sulfate ions contained in the solution by an electrolytic reaction. An electrolytic reaction device that generates sulfate ions to regenerate a persulfuric acid solution, and a circulation line that circulates the persulfuric acid solution while performing the cleaning and the electrolytic reaction between the cleaning device and the electrolytic reaction device. The electrolytic reaction apparatus is configured such that at least an anode of the anode and the cathode included in the apparatus is conductive diamond, and the anode and the cathode are separated by a diaphragm, and the anode and the cathode are separated during the circulation. persulfate solution concentration of sulfuric acid is cooled in 8M~18M between diaphragm is liquid passage, sulfuric acid concentration independent of the circulation line between the diaphragm and the cathode 0 As sulfuric acid solution 1M~18M mediated, characterized in that it comprises a circulation line for the cathode circulating a sulfuric acid solution.

The invention of the sulfuric acid recycling type cleaning system according to claim 2 is the invention according to claim 1 , wherein in the circulation line, a relatively low temperature persulfuric acid solution feed from the electrolytic reaction device and the cleaning device are used. It has a heat exchange means for exchanging heat with the return liquid of the relatively high temperature persulfuric acid solution.

The invention of claim 3, wherein the sulfuric acid recycle type cleaning system is the invention according to claim 1 or 2, characterized in that the flow path in the circulation line consists of quartz or tetrafluoroethylene.

The invention of the sulfuric acid recycling type cleaning system according to claim 4 is characterized in that in the invention according to any one of claims 1 to 3 , the sulfuric acid recycling type cleaning system has a thermal decomposition apparatus for decomposing the removed material removed from the semiconductor substrate by the cleaning. And

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

The invention of claim 6, wherein the sulfuric acid recycle type cleaning system is the invention according to any one of claims 1 to 5, and the total organic carbon concentration (TOC) production rate of organic contaminants by washing in the washing device, wherein the ratio of persulfate production rate in the electrolysis apparatus (persulfuric acid production rate [g / l / hr] / (the TOC generation rate cleaning tank [g / l / hr]) is electrolytically to consist of 10 to 500 It is characterized by that.
The sulfuric acid recycling type cleaning system according to claim 7 is the invention according to any one of claims 1 to 6, wherein the semiconductor substrate is a resist attached to the semiconductor substrate prior to cleaning with the persulfuric acid solution. It is characterized in that it has not undergone a pretreatment step of oxidizing and ashing.

That is, according to the present invention, persulfate ions in the cleaning solution self-decompose and generate oxidizing power, and contaminants and the like of the semiconductor substrate 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. Moreover, in the electrolytic reaction apparatus, the persulfate solution to be regenerated is passed only between the anode and the diaphragm provided in the electrolytic reaction apparatus and not to the cathode side. It is possible to prevent persulfate ions from being reduced on the cathode side and efficiently generate persulfate ions. In addition, electrolysis is performed through the persulfuric acid solution and an electrolytic solution interposed between the diaphragm and the cathode.
The persulfuric acid solution regenerated as described above is sent to a cleaning device through a circulation line, and the semiconductor substrate is effectively peeled and cleaned with high-concentration persulfuric acid as described above. Persulfuric acid is repeatedly 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. On the other hand, in the electrolytic reaction apparatus, the lower the solution temperature, the better the efficiency of producing persulfuric acid and the smaller the wear of the electrode. In the present invention, since the cleaning device and the electrolytic reaction device are separated, the temperature of the solution electrolyzed in the electrolytic reaction device can be kept lower than the temperature of the cleaning solution. Can increase the efficiency.

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

Moreover, the persulfuric acid solution electrolyzed by the electrolytic reaction apparatus can be cooled to an appropriate temperature by an appropriate cooling means. Examples of the cooling means include air coolers and water coolers. The appropriate temperature as the solution to be electrolyzed can be in the range of 10 to 90 ° C. When the temperature range is exceeded, the electrolysis efficiency decreases and the wear of the electrode also increases. On the other hand, if the temperature is below the above temperature range, the heat energy for heating to the washing tank temperature of 130 ° C. becomes enormous, and the piping path for heat exchange becomes significantly longer, which is not practical. For the same reason, it is more desirable to set the lower limit to 40 ° C. and the upper limit to 80 ° C. Note that the electrolyte solution interposed between the diaphragm and the cathode is preferably set to a temperature of 90 ° C. or lower for the same reason as described above. Since the electrolytic solution is not sent to the washing tank, it is not necessary to set a lower limit temperature unlike the persulfuric acid solution. Moreover, you may make it give the cooling effect | action with respect to a persulfuric-acid solution, or a constant temperature action to this electrolyte solution.
The heating means and cooling means described above may be attached to a cleaning device or an electrolytic reaction device, or may be provided in a circulation line. Further, another line may be provided in the cleaning device or the electrolytic reaction device to heat or cool the solution.

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

In addition, organic substances such as a resist that have been included in the persulfuric acid solution by cleaning may be decomposed by a thermal decomposition apparatus provided outside the circulation line system or the circulation line system .

In the above system, the solution electrolyzed on the anode side of the electrolytic reaction apparatus contains sulfate ions, and the production efficiency of persulfate ions in the electrolytic reaction apparatus is greatly influenced by the sulfuric acid concentration. Specifically, the persulfuric acid generation efficiency increases as the sulfuric acid concentration decreases. On the other hand, when the sulfuric acid concentration is lowered, the solubility of an organic compound such as a resist is lowered and it is difficult to peel off from the semiconductor substrate . From these viewpoints, the sulfuric acid concentration of the solution used in the circulation line is in the range of 8M to 18M . For the same reason, it is more desirable that the lower limit is 12M and the upper limit is 17M.
On the other hand, the electrolytic solution of the cathode side, yo if there is electrical conductivity as the present invention Iga, Ru with a sulfuric acid solution as the persulfate solution impurities as little as possible contamination through the septum. Concentration in sulfuric acid solution in the range from 0.1M to 18M.

In the electrolytic reaction apparatus, electrolysis is performed by pairing an anode and a cathode. The anode and cathode may include an anode and a cathode that appear when energized in the bipolar electrode, in addition to an electrode that is electrically connected directly to a power source. As a material for these electrodes, when platinum, which is generally widely used as an electrode, is used as the anode of the electrolytic reaction apparatus of the present invention, there is a problem that persulfate ions cannot be efficiently produced and platinum is eluted. is there. On the other hand, the diamond electrode can efficiently generate persulfate ions and has little electrode wear. Therefore, at least an anode that generates sulfate ions is formed of a diamond electrode among the electrodes of the electrolytic reaction apparatus . It is more desirable that both the anode and the cathode are composed of diamond electrodes.

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

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

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

In the electrolytic treatment performed using the conductive diamond electrode, the current density on the surface of the conductive diamond electrode is set to 10 to 100,000 A / m ^2, and a solution containing sulfate ions is parallel to the diamond electrode surface and the liquid passage speed is set. It is desirable to perform contact treatment at 1 to 10,000 m / hr.
In addition, the persulfuric acid production rate [g / l / hr] in the electrolytic reaction device is 10 to 500 times that of the TOC production rate [g / l / hr] produced by the resist stripping and dissolving in the cleaning device. It is desirable to set the electrolysis conditions so that This balances the consumption and generation of persulfuric acid, and allows efficient cleaning and efficient electrolytic treatment. For the same reason, it is desirable to set the lower limit to 20 and the upper limit to 300.

In the cleaning system of the present invention, as described above, the diaphragm is disposed between the anode and the cathode in the electrolytic reaction apparatus. The material of the diaphragm may be any material as long as it allows ions to pass therethrough and does not hinder electrolysis in the electrolytic reaction apparatus, and the present invention is not limited to a specific material, but includes fluororesin-based and hydrocarbon-based materials. It is desirable to use a fluororesin that is less susceptible to dissolution or composition change due to persulfuric acid or concentrated sulfuric acid. A fluororesin-based cation exchange membrane (such as “Nafion” (trademark)) that allows the passage of cations and inhibits the passage of anions is preferred.
In addition, the manufacturing method of a diaphragm, thickness, the number of sheets, etc. are not specifically limited as this invention, It can select suitably.

In the cleaning system of the present invention, a silicon wafer, glass substrate for liquid crystal, Ri preferably der in electronic material applications for the cleaning process intended for a substrate such as a photomask substrate, and more specifically, on the semiconductor substrate It uses a stripping process of organic compounds such as deposited resist residue. 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 sulfuric acid recycling type cleaning system of the present invention, the cleaning apparatus for cleaning the semiconductor substrate using the heated persulfuric acid solution as the cleaning liquid, and the persulfate ions from the sulfate ions contained in the solution by the electrolytic reaction. And a recirculation line for circulating the persulfuric acid solution while performing the washing and the electrolytic reaction between the washing device and the electrolytic reaction device. In the electrolytic reaction apparatus, at least the anode of the anode and the cathode included in the apparatus is a conductive diamond, and the anode and the cathode are separated by a diaphragm, and the anode and the diaphragm are separated during the circulation. sulfuric acid concentration between are persulfate solution through solution cooled in 8M～18M, sulfuric acid concentration independent of the circulation line between the diaphragm and the cathode 0.1M~ So as to intervene sulfuric acid solution 8M is, since comprise a circulation line for the cathode circulating a sulfuric acid solution, the efficiency on site by electrolysis reactor persulfate solution to enhance the release effect while repeatedly using sulfuric acid solution Can be regenerated and used for cleaning. In addition, efficient cleaning can be continued without requiring addition of a chemical solution such as hydrogen peroxide or ozone from the outside.

(Embodiment 1)
Below, one Embodiment of this invention is described based on FIG.
A cleaning tank 1 and an electrolytic reaction device 10 corresponding to the cleaning device of the present invention are connected by a return pipe 4 and a feed pipe 5. The return pipe 4 and the feed pipe 5 each have at least an inner surface made of tetrafluoroethylene, and the return pipe 4 is provided with a liquid feed pump 6 for feeding the persulfuric acid solution 2. The return pipe 4, the feed pipe 5 and the liquid feed pump 6 constitute a circulation line of the present invention. A heat exchanger 7 corresponding to the heat exchanging means of the present invention is interposed between the return pipe 4 and the feed pipe 5, and the solution flowing through the return pipe 4 by the heat exchanger 7 and the feed pipe The solution flowing through 5 can exchange heat with each other. Note that at least the inner surface of the flow path (not shown) in the heat exchanger 7 is made of tetrafluoroethylene. As described above, the flow path of the return pipe 4, the feed pipe 5, and the heat exchanger 7 is made of tetrafluoroethylene or the like that is resistant to persulfuric acid, so that wear due to persulfuric acid can be avoided.
The washing tank 1 includes a heater 3 for heating the contained sulfuric acid solution or persulfuric acid solution 2, and ultrapure water replenishment for replenishing the sulfuric acid solution or persulfuric acid solution 2 with ultrapure water. A line 25 is provided.

Next, details of the electrolytic reaction apparatus 10 will be described. As shown in FIG. 2, the electrolytic reaction apparatus 10 includes an electrolytic reaction tank 11, and an anode 12 and a cathode 13 are disposed in the electrolytic reaction tank 11, and a gap is further provided between the anode 12 and the cathode 13. A bipolar electrode 14 is disposed at the position. In this embodiment, the electrodes 12, 13, and 14 are constituted by diamond electrodes having a diameter of 15 cm. The diamond electrode is manufactured by forming a diamond thin film on a substrate and doping boron in a range of preferably 50 to 20,000 ppm with respect to the carbon content of the diamond thin film. Further, it may be a self-supporting type by removing the substrate after forming the thin film.
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 15 is connected to the anode 12 and the cathode 13, thereby enabling DC electrolysis in the electrolytic reaction tank 11. Further, a diaphragm 16 is disposed between the anode 12 and the bipolar electrode 14, and a diaphragm 17 is disposed between the bipolar electrode 14 and the cathode 13 so that adjacent electrodes are isolated from each other. The diaphragms 16 and 17 are made of a fluororesin ion exchange membrane.

  The return pipe 4 is branched into two when connected to the electrolytic reaction tank 11, and is one end between the anode 12 and the diaphragm 16 and between the bipolar electrode 14 and the diaphragm 17 (hereinafter referred to as “anode chamber”). It is connected to. Similarly, the feed pipe 5 branches into two when connected to the electrolytic reaction tank 11 and is connected to the other end side of the anode chamber. With the above configuration, the persulfuric acid solution moving through the return pipe 4 and the feed pipe 5 is passed through the anode chamber. On the other hand, at one end between the diaphragm 16 and the bipolar electrode 14 and between the diaphragm 17 and the cathode 13 (hereinafter referred to as “cathode chamber”), an electrolyte return pipe 21 connected to the electrolyte storage tank 20 branches into two. The electrolyte feed pipe 23 is branched into two and connected to the other end side of the cathode chamber. The other end of the electrolytic solution feeding pipe 23 is connected to the electrolytic solution storage tank 20, and a liquid feeding pump 22 is provided in the electrolytic solution return pipe 21, thereby providing a space between the electrolytic storage tank 20 and the electrolytic reaction tank 10. The electrolyte can be circulated. In this embodiment, a sulfuric acid solution is used as the electrolytic solution and is stored in the electrolytic solution storage tank 20.

Next, the operation of the sulfuric acid recycling type cleaning system having the above configuration will be described.
In the washing tank 1, sulfuric acid having a sulfuric acid concentration of 10 to 18 M is accommodated, and ultrapure water is mixed with the sulfuric acid so that the volume ratio is 5: 1 to obtain a sulfuric acid solution. This is sequentially fed to the electrolytic reaction tank 11 by the liquid feed pump 6. On the other hand, 1 M to 18 M sulfuric acid is accommodated in the electrolytic storage tank 20, and is sequentially fed to the electrolytic reaction tank 11 by the liquid feed pump 22. In the electrolytic reaction tank 11, when the anode 12 and the cathode 13 are energized by the DC power supply 14, the bipolar electrode 13 is polarized, and the cathode (anode 12 side surface) and the anode (cathode 13 side surface) appear. The solution fed to the electrolytic reaction tank 11 through the return pipe 4 by the liquid feed pump 6 is passed through the anode chamber. At this time, it is desirable to set the output of the liquid feed pump 6 so that the liquid flow rate is 1 to 10,000 m / 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.}
The sulfuric acid solution fed to the electrolytic reaction tank 11 through the electrolyte return pipe 21 by the liquid feed pump 22 is passed through the cathode chamber. In this case, it is not particularly necessary to specify the liquid flow velocity, and it may be in the range of 1 to 10,000 m / hr.

When the solution is energized in the electrolytic reaction tank 11, sulfate ions in the solution flowing through the circulation line are oxidized in the anode chamber to generate persulfate ions and the persulfate solution 2 is regenerated. At this time, since the persulfate ions are prevented from moving to the cathode by the diaphragms 16 and 17, it can be avoided that the persulfate ions are reduced on the cathode side and returned to the sulfate ions. In the cathode chamber, hydrogen ions are reduced to generate hydrogen gas, which is discharged out of the electric reaction tank 11 as the liquid passes.
The persulfuric acid solution 2 in the anode chamber is fed from the feed pipe 5 to the cleaning tank 1, and a high-concentration persulfuric acid solution 2 is obtained in the cleaning tank 1. Although the persulfate ion concentration gradually decreases in the washing tank 1 due to autolysis, the solution circulates between the anode chamber of the electrolytic reaction tank 11 and is electrolyzed in the electrolytic reaction tank 11 to generate persulfate ions. High persulfate ion concentration is maintained. In this embodiment, the process of producing persulfuric acid from sulfuric acid at the time of start-up has been described. However, as the present invention, persulfuric acid may be prepared from the beginning. However, in terms of producing persulfuric acid on-site, it is advantageous to produce persulfuric acid using an electrolytic reactor.

  Further, the persulfuric acid solution 2 in the cleaning tank 1 can be further heated to a temperature suitable for cleaning by being heated by the heater 3. In the state where the temperature of the persulfuric acid solution 2 serving as the cleaning liquid is about 130 ° C. in the cleaning tank 1 due to the above temperature rise, the semiconductor wafer 30 as the material to be cleaned is immersed in the cleaning tank 1 to start cleaning. . In the cleaning tank 1, a high oxidation action is obtained by self-decomposition of persulfate ions, and contaminants and the like on the semiconductor wafer 30 are effectively peeled off and transferred to the persulfate solution 2. Furthermore, the organic compound such as a resist is thermally decomposed in the persulfuric acid solution 2 and the cleanliness of the persulfuric acid solution 2 is increased. The persulfuric acid in the washing tank 1 was sent to the electrolytic reaction tank 11 by the return pipe 4 and the liquid feed pump 6, and persulfate ions were generated from the sulfate ions in the anode chamber as described above, and decreased by self-decomposition. The persulfuric acid solution 2 is regenerated by increasing the persulfuric acid concentration.

  Further, when the persulfuric acid solution 2 moves from the washing tank 1 toward the electrolytic reaction tank 11 through the return pipe 4, the persulfuric acid solution 2 is moved in the electrolytic reaction tank 11 to move the feed pipe 5. In the meantime, heat exchange is performed in the heat exchanger 7. The persulfuric acid solution 2 fed from the washing tank 1 is heated to about 130 ° C. so as to be suitable for washing. On the other hand, the persulfuric acid solution 2 fed from the electrolytic reaction tank 10 has a temperature of about 40 ° C. When these persulfuric acid solutions 2 are heat-exchanged, the persulfuric acid solution 2 moving through the return pipe 4 is lowered to a temperature close to 40 ° C., whereas the persulfuric acid solution 2 moving through the feed pipe 5 is close to 130 ° C. Heated to temperature. The persulfuric acid solution 2 that is heat-exchanged by the heat exchanger 7 and moves through the return pipe 4 is then gradually cooled by natural cooling to a temperature of about 40 ° C. suitable for the electrolytic reaction. In addition, when it is desired to reliably lower the temperature, a cooling means for forcibly cooling the electrolytic reaction tank 11 by water cooling or air cooling can be provided. Further, in the cathode chamber of the electrolytic reaction tank 11, a constant temperature sulfuric acid solution 24 circulates, and the sulfuric acid solution 24 makes it easy to maintain the temperature in the electrolytic reaction tank 11 at an appropriate temperature. The means for cooling the solution in (except for the heat exchanger 7) can be eliminated.

  The persulfuric acid solution 2 that is heat-exchanged by the heat exchanger 7 and moves through the feed pipe 5 is sent to the washing tank 1 and mixed with the persulfuric acid solution 2 remaining in the washing tank 1. When the temperature of the persulfuric acid solution 2 in the cleaning tank 1 has decreased, the temperature can be raised to an optimum temperature for cleaning by heating with the heater 3. As described above, the persulfuric acid solution 2 is cooled when being sent from the washing tank 1 to the electrolytic reaction tank 10, electrolyzed, and then heated when being returned from the electrolytic reaction tank 10 to the washing tank 1. The amount of heat that is cooled in this one cycle is almost equal to the amount of heat that is heated, so a highly efficient heat exchanger 7 is incorporated, and heat energy is applied from the outside for the amount of heat release, so that the persulfuric acid solution is efficiently 2 temperature adjustment can be performed.

  By cleaning the semiconductor wafer 30 by the sulfuric acid recycling type cleaning system, it is effective to regenerate the persulfuric acid solution 2 by repeatedly using the sulfuric acid solution without the need for adding hydrogen peroxide or ozone. Washing can be continued.

(Embodiment 2)
Next, another embodiment will be described with reference to FIG.
In addition, in this Embodiment 2, the same code | symbol is attached | subjected about the structure similar to the said Embodiment 1, and the description is abbreviate | omitted or simplified.
In this embodiment, electrolytic reaction tanks 11 a and 11 b provided in the electrolytic reaction apparatus 10 are connected to the cleaning tank 1 by a return pipe 4 and a feed pipe 5. A liquid feed pump 6 is interposed in the return pipe 4, and a heat exchanger 7 is provided between the return pipe 4 and the feed pipe 5 as in the first embodiment.

The electrolytic reaction tanks 11a and 11b have the same structure, and are each provided with a pair of an anode 12a, a cathode 13a, an anode 12b, and a cathode 13b. Bipolar electrodes 14a and 14b are disposed between the anodes 12a and 12b and the cathodes 13a and 13b, respectively. These anodes 12a and 12, cathodes 13a and 13b, and bipolar electrodes 14a and 14b are composed of diamond electrodes having the same configuration as in the first embodiment. The anode 12a and the cathode 13a and the anode 12b and the cathode 13b are connected in parallel to the DC power source 15, thereby enabling DC electrolysis in the electrolytic reaction tanks 11a and 11b.
The anodes 12a, 12b and the bipolar electrodes 13a, 13b are separated by diaphragms 16a, 16b, respectively. The bipolar electrodes 13a, 13b and the cathodes 13a, 13b are separated by diaphragms 17a, 17b, respectively. ing. The diaphragms 16a to 17b are made of the same material and are made of an ion exchange membrane made of a fluororesin system.

  The electrolytic reaction tank 11a and the electrolytic reaction tank 11b are connected in series, the return pipe 4 is branched into two, and between the anode 12a and the diaphragm 16a and between the bipolar electrode 14a and the diaphragm 17a in the electrolytic reaction tank 11a. It is connected to one end of the space (referred to as anode chamber a). The other end side of the anode chamber a is connected to one end of the electrolytic reaction tank 11b between the anode 12b and the diaphragm 16b and between the bipolar electrode 14b and the diaphragm 17b (referred to as the anode chamber b) through the connecting pipe 110. . A feed pipe 5 branched in two is connected to the other end side of the anode chamber b.

Also in this embodiment, as in the first embodiment, an electrolyte storage tank 20, an electrolyte return pipe 21, a liquid feed pump 22, and an electrolyte feed pipe 23 are provided.
The electrolyte return pipe 21 is branched into two and connected to one end of the electrolytic reaction tank 11a between the diaphragm 16a and the bipolar electrode 14a and between the diaphragm 17a and the cathode 13a (referred to as a cathode chamber a). The other end side of the cathode chamber a is connected to one end between the diaphragm 16b and the bipolar electrode 14b and between the diaphragm 17b and the cathode 13b (referred to as the cathode chamber b) in the electrolytic reaction tank 11b through a connecting tube 111. . The other end side of the cathode chamber b is connected to an electrolyte feeding pipe 23 branched in two.

Next, the operation of the sulfuric acid recycling type cleaning system will be described.
In the cleaning tank 1, 8M to 18M sulfuric acid is accommodated in the same manner as in the first embodiment, and is heated to about 130 ° C. by the heater 3. The electrolyte storage tank 20 also contains 0.1M to 18M sulfuric acid.
The sulfuric acid solution in the cleaning tank 1 is sent to the anode chamber a of the electrolytic reaction tank 11a by the liquid feed pump 6. In the electrolytic reaction tanks 11a and 11b, the bipolar electrodes 13a and 13b are polarized by energizing the anode 12a and the cathode 13a and between the anode 12b and the cathode 13b by the DC power source 14. In addition, the liquid flow rate in the electrolytic reaction tanks 11a and 11b is controlled to be 1 to 10,000 m / hr, and the current density on the surface of the diamond electrode is 10 to 100,000 A / m ² . Further, the sulfuric acid solution in the electrolytic solution storage tank 20 is sent to the cathode chamber a of the electrolytic reaction tank 11a by the liquid feed pump 23.

In the solution passing through the anode chamber a of the electrolytic reaction tank 11 a, persulfate ions are generated from sulfate ions, and are further sent to the anode chamber b of the electrolytic reaction tank 11 b via the connecting pipe 110. On the other hand, the electrolytic solution 24 flowing through the cathode chamber a in the electrolytic reaction tank 11a contributes to the electrolytic reaction, and then is sent to the cathode chamber b of the electrolytic reaction tank 11b through the connecting tube 111.
Also in the electrolytic reaction tank 11b, persulfate ions are similarly generated from sulfate ions in the anode section b, and a persulfate solution 2 having a higher concentration is obtained. The high-concentration persulfuric acid solution 2 is sent to the washing tank 1 through the feed pipe 5. Further, the electrolytic solution 24 that has contributed to the electrolytic reaction in the cathode section b of the electrolytic reaction tank 11 b is sent to the electrolytic solution storage tank 20 through the electrolytic solution feed pipe 23.

In the cleaning tank 1, the semiconductor wafer 30 is cleaned with the high-concentration persulfuric acid solution 2 in the same manner as in the above embodiment. In the washing tank 1, the persulfuric acid solution 2 in which the persulfuric acid concentration is gradually reduced by autolysis is sent to the anode section a of the electrolytic reaction tank 11a and the anode section b of the electrolytic reaction tank 11b through the return pipe 4 and the liquid feed pump 6. Liquidized, electrolyzed and regenerated. When the return pipe 4 is moved, heat is exchanged in the heat exchanger 7 with the persulfuric acid solution 2 which is subjected to electrolytic treatment in the electrolytic reaction tank 11b and moves through the feed pipe 5, and each is washed. It is adjusted to a suitable temperature and a temperature suitable for the electrolytic reaction. The persulfuric acid solution 2 that moves through the feed pipe 5 is sent to the washing tank 1, and then the temperature is adjusted to the optimum temperature for washing by heating with the heater 3. Also in this embodiment, effective cleaning can be continued while regenerating the persulfuric acid solution 2 by repeatedly using the sulfuric acid solution.
The present invention has been described above based on the first and second embodiments. However, the present invention is not limited to the description of the above embodiment, and can be modified without departing from the scope of the present invention. .

Next, using the sulfuric acid recycle type cleaning system shown in FIG. 1, the cleaning process was performed under the following conditions.
A high-concentration sulfuric acid solution adjusted at a ratio of 98 l concentrated sulfuric acid 40 l and ultrapure water 10 l was accommodated in the washing tank and heated to 130 ° C. In the electrolytic reaction tank, 10 conductive diamond electrodes doped with boron (boron doping amount: 5,000 ppm) are incorporated into a Si substrate having a diameter of 15 cm and a thickness of 1 mm, and two tanks each having a Nafion film are interposed between the electrodes. Arranged in series. The effective electrolysis area for electrolysis was 30 dm ^{2 as} a whole, and electrolysis was performed at 40 ° C. with a current density set to 3,000 A / m ² . Sampling the electrolytic reactor outlet water confirmed that the persulfuric acid production rate was 3.5 g / l / hr. In the cleaning tank, a 5-inch silicon wafer with a resist was immersed at 60 wafers / cycle for 10 minutes as an immersion cycle, and the resist was dissolved (TOC generation rate was 0.07 g / l / hr). This solution was circulated between the washing tank and the electrolytic reaction tank at a flow rate of 1 l / min (liquid passage speed was 80 m / hr) with a liquid feed pump. When the silicon wafer with resist was immersed, the solution in the cleaning tank was colored brown and the TOC concentration was 36 mg / l. The concentration was below the detection limit. Although such wafer cleaning was continued for 8 hours (the number of cleaned wafers was 2,880), the resist stripping effect of the high-concentration sulfuric acid solution was good, and the TOC concentration was also below the detection limit. Therefore, it continued for another 32 hours (11,520 cleaning wafers, 14,400 total processing wafers), but the resist stripping effect of the high-concentration sulfuric acid solution was good, and the TOC concentration was below the detection limit. It was. Compared to the case where no diaphragm was used, the total number of processed sheets was 1.2 times.

(Comparative Example 1)
A solution containing 40 l of 98% concentrated sulfuric acid and 10 l of 35% hydrogen peroxide solution was heated and maintained at 130 ° C. in a washing tank. The resist-coated wafer was immersed in this solution in the same immersion cycle as in Example 2 to dissolve the resist. Up to the first 6 cycles (300 wafers to be cleaned), the solution was colored brown immediately after immersion in the wafer, but became colorless and transparent in less than 10 minutes, and the TOC concentration became the detection limit. However, for the next 50 sheets, the solution remained brown even after 10 minutes immediately after immersion, and a residual TOC groove of 30 mg / l was observed. Therefore, 10 l of the solution in the washing tank was drawn out, and 10 l of hydrogen peroxide solution was further added, and the solution was heated and maintained at 130 ° C. The wafer immersion was continued again. Up to the first 2 cycles (100 wafers to be cleaned), the solution was colored brown immediately after immersion in the wafer, but became colorless and transparent in a little less than 10 minutes, and the TOC concentration became the detection limit. However, for the next 50 sheets, the solution remained brown even after 10 minutes immediately after immersion, and a residual TOC concentration of 30 mg / l was observed. Again, 10 l of the solution in the washing tank was withdrawn, and 10 l of hydrogen peroxide solution was additionally added. Although the wafer immersion was continued, when 50 wafers were immersed, the resist peeling dissolution effect was poor and the resist remained on the wafer even after 10 minutes. When the total number of processed wafers was 400, the entire solution had to be replaced.

Under the conditions of Example 1, a cleaning test was conducted by changing the temperature of the persulfuric acid solution in the cleaning tank. Other conditions are the same as in the first embodiment.
As a result, in the cleaning example in which the cleaning liquid was heated to 90 ° C., the resist peeling rate on the wafer was slow in the first cycle, and the resist remained on the wafer, so that the cleaning was not sufficiently performed. On the other hand, in the cleaning example (Example 2) performed by heating the cleaning liquid to 130 ° C., the resist stripping rate is high, and the persulfuric acid generation rate (3) sufficient for the TOC generation rate (0.07 g / l / hr). 0.5 g / l / hr) can be secured, and an effective cleaning effect was obtained. In the cleaning example in which the cleaning liquid was heated to 160 ° C., the persulfuric acid generation rate (3.5 g / l / hr) sufficient for the TOC generation rate (0.07 g / l / hr) in the first cycle. ) Was ensured, but the rate of self-decomposition of persulfuric acid in the washing tank was large, so that sufficient persulfuric acid did not remain to remove TOC, and 30 mg / l of TOC concentration remained in the solution. Therefore, it is clear that the temperature of the cleaning liquid is desirably 100 ° C to 150 ° C.

Next, a cleaning test was performed under the conditions of Example 1 while changing the temperature of the solution in the electrolytic reaction tank. Other test conditions are the same as in Example 1.
As a result, in the example in which the electrolytic reaction tank was set to 5 ° C., the persulfuric acid production rate was 5 g / l / hr, and a sufficient amount of persulfuric acid was secured for the TOC production rate of 0.07 g / l / hr. Since the washing temperature is 130 ° C., it is necessary to heat for 125 ° C., and not only a great amount of heat energy needs to be input, but also a long piping route is required. Most of it was consumed, and in the first cycle, a TOC concentration of 30 mg / l remained in the solution. On the other hand, in the examples in which the temperature of the solution in the electrolytic reaction tank was 10 ° C., 40 ° C., 80 ° C., and 90 ° C., the persulfuric acid production rates were 4.5 g / l / hr, 3.5 g / l / hr, 1. At 4 g / l / hr and 1.1 g / l / hr, persulfate ions were efficiently generated. Further, no electrode wear was observed even after 1,000 hours of electrolytic treatment. On the other hand, in the example in which the solution temperature in the electrolytic reaction tank was 100 ° C., the persulfuric acid production rate was 0.3 g / l / hr, and the production of persulfate ions was clearly reduced. That is, (persulfuric acid production rate [g / l / hr]) / (TOC production rate [g / l / hr]) <10, and a sufficient oxidative decomposition effect was not obtained. Further, the conductive diamond layer was peeled off from the Si substrate by an electrolytic reaction for 500 hours. Therefore, it is clear that the temperature of the solution subjected to electrolysis is preferably 10 to 90 ° C.

Next, under the conditions of Example 1, a cleaning test was performed by changing the persulfuric acid production rate by changing the current density in the electrolytic reaction tank. The other test conditions are the same as in Example 1.
As a result, the current density as shown in Table 1 is sufficient persulfate production rate obtained for TOC production rate in the range of 10~100,000A / ^{m 2,} good cleaning effect was obtained.

Next, under the conditions of Example 1, a washing test was performed by changing the persulfuric acid production rate by changing the liquid flow rate in the electrolytic reaction tank. The other test conditions are the same as in Example 1.
As a result, it became as shown in Table 2. That is, when the liquid flow rate was 0.3 m / hr, bubbles were accumulated in the electrolysis cell and the electrolysis operation was impossible. Further, when the liquid flow rate was 20,000 m / hr, the piping path in the heat exchanger became enormous, and the device design could not be performed. When the liquid flow rate was in the range of 1 to 10,000 m / hr, a sufficient persulfuric acid production rate was obtained relative to the TOC production rate, and a good cleaning effect was obtained.

It is the schematic which shows the system in one Embodiment of this invention. It is the detail drawing of an electrolytic reaction apparatus similarly. It is the schematic which shows the system in other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Washing tank 2 Persulfuric acid solution 3 Heater 4 Return pipe 5 Feeding pipe 6 Liquid feed pump 7 Heat exchanger 10 Electrolytic reaction apparatus 11, 11a, 11b Electrolytic reaction tank 12, 12a, 12b Anode 13, 13a, 13b Cathode 14, 14a , 14b Bipolar electrodes 16, 16a, 16b Diaphragm 17, 17a, 17b Diaphragm 20 Electrolyte storage tank 21 Electrolyte return pipe 22 Liquid feed pump 23 Electrolyte feed pipe 30 Semiconductor wafer

Claims (7)

A cleaning apparatus for cleaning a semiconductor substrate using a heated persulfuric acid solution as a cleaning liquid, an electrolytic reaction apparatus for regenerating a persulfuric acid solution by generating persulfate ions from sulfate ions contained in the solution by an electrolytic reaction, and the cleaning apparatus A circulation line for circulating the persulfuric acid solution while performing the washing and the electrolytic reaction, and the electrolytic reaction device includes at least an anode among an anode and a cathode provided in the device. Is a conductive diamond, and the anode and the cathode are separated by a diaphragm, and during the circulation, a cooled persulfuric acid solution having a sulfuric acid concentration of 8M to 18M is passed between the anode and the diaphragm. is liquid, as sulfuric acid solution independently sulfuric acid concentration is 0.1M~18M from said circulation line between the diaphragm and the cathode is interposed,循for the cathode circulating a sulfuric acid solution Sulfuric acid recycle type cleaning system, characterized in that it comprises a line. Heat exchange for exchanging heat between a relatively low temperature persulfuric acid solution feed from the electrolytic reaction device and a relatively high temperature persulfuric acid solution return from the cleaning device in the circulation line. sulfuric acid recycle type cleaning system according to claim 1, characterized in that it comprises means. The sulfuric acid recycle type cleaning system according to claim 1 or 2 , wherein the flow path in the circulation line is made of quartz or tetrafluoroethylene. The sulfuric acid recycle type cleaning system according to any one of claims 1 to 3 , further comprising a thermal decomposition apparatus for decomposing a removed material removed from the semiconductor substrate by the cleaning. The cleaning system according to claim 1 , wherein the conductive diamond electrode provided in the electrolytic reaction device is a self-supporting conductive diamond electrode in which the substrate is removed after being laminated on the substrate. Ratio of total organic carbon concentration (TOC) generation rate of organic contaminants by cleaning in the cleaning device and persulfuric acid generation rate in the electrolytic device (persulfuric acid generation rate [g / l / hr] / (in the cleaning tank The sulfuric acid recycle type cleaning system according to any one of claims 1 to 5 , wherein electrolysis is performed so that a TOC generation rate [g / l / hr] is 10 to 500. The semiconductor substrate according to any one of claims 1 to 6, wherein the semiconductor substrate has not undergone a pretreatment step of oxidizing and ashing a resist adhering to the semiconductor substrate prior to cleaning with the persulfuric acid solution. The sulfuric acid recycling type cleaning system described in Crab.

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