JP2006278838A - Sulfuric acid recycling type cleaning system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently clean a cleaning object such as a semiconductor wafer. <P>SOLUTION: This system is provided with a cleaning apparatus 1 for cleaning the cleaning object with a persulfuric acid solution; electrolytic reaction apparatuses 10, 11, 12, 13 and 14 for regenerating the persulfuric acid solution by an electrolytic reaction; cleaning apparatus transferring line 5 for transferring a solution from the cleaning apparatus 1; cleaning apparatus return line 7 for returning the solution to the cleaning apparatus 1; electrolytic reaction apparatus returning line 15 for transferring the solution from the electrolytic reaction apparatus; electrolytic reaction apparatus returning line 17 for returning the solution to the electrolytic reaction apparatus; and mixing line 20 for converging the line 5 with the line 15, in an upstream end and dividing the line into the line 7 and the line 17 in a downstream end. The sulfuric acid solution is repeatedly utilized and the persulfuric acid solution improving a resist peeling effect is regenerated in the electrolytic reaction apparatus, and a resist solute matter is decomposed and supplied to the cleaning apparatus again. Thus, efficient cleaning can be continued without requiring addition of a chemical liquid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sulfuric acid recycle type cleaning system that regenerates persulfuric acid 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 high peeling effect. Is.

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

  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. For this reason, in the cleaning using the above-described SPM method or SOM method, as a pretreatment step of the SPM method or SOM method, dry etching or an ashing process is used to oxidize and ash the organic resist in advance. A process is incorporated. There is a problem that pre-processing such as dry etching or ashing process damages the wafer or increases the cost of the apparatus.

  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. It is an object of the present invention to provide a sulfuric acid recycle type cleaning system capable of continuously obtaining a good cleaning action.

  That is, among the sulfuric acid recycle type cleaning systems of the present invention, the invention according to claim 1 is the above-mentioned solution by electrolyzing a cleaning apparatus for cleaning a material to be cleaned using a persulfuric acid solution as a cleaning liquid, and the solution used for cleaning. An electrolytic reaction device for regenerating a persulfate solution by generating persulfate ions from sulfate ions contained in a cleaning device, a cleaning device feed line for discharging the solution from the cleaning device, a cleaning device return line for returning the solution to the cleaning device, The electrolytic reaction device feed line for sending the solution from the electrolytic reaction device, the electrolytic reaction device return line for returning the solution to the electrolytic reaction device, the washing device feed line and the electrolytic reaction device feed line merge at the upstream end, and downstream And a mixing line for diverting the cleaning device return line and the electrolytic reaction device return line at the end.

  The sulfuric acid recycle type cleaning system according to claim 2 is characterized in that, in the invention according to claim 1, the flow of the solution in the mixing line is a plug flow having a flow velocity of 0.1 m / second or less.

  The invention of the sulfuric acid recycling type cleaning system according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the time for which the solution flows through the mixing line is 20 minutes or less.

  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, a heating device for heating the cleaning liquid to 120 to 150 ° C. is provided.

  The invention of the sulfuric acid recycle type cleaning system according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, the temperature of the electrolytically reacted solution is in the range of 10 to 90 ° C.

  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 solution is 8M or more.

  The sulfuric acid recycling type cleaning system according to claim 7 is characterized in that, in the invention according to any one of claims 1 to 6, a conductive diamond electrode is used for at least the anode among the electrodes used in the electrolytic reaction apparatus. And

  According to the present invention, in the cleaning apparatus, persulfate ions in the cleaning liquid self-decompose to generate an oxidizing power, and in addition to the cleaning action by sulfuric acid, the contamination of the material to be cleaned by the oxidizing power by persulfuric acid is effective. It is peeled and washed. For example, when cleaning a wafer, the resist adhering to the wafer is peeled off by the cleaning action and dissolved in the cleaning liquid. A part of the lysate is decomposed by the oxidizing action of persulfuric acid in the cleaning device.

  The solution used for washing circulates through the washing device feed line, the mixing line, and the washing device return line. On the other hand, in an electrolytic reaction apparatus, an anode and a cathode are immersed in a solution containing sulfate ions, and current is passed between the electrodes to perform electrolysis, whereby sulfate ions are oxidized to produce persulfate ions, and the concentration of persulfate is increased. The persulfuric acid solution having a high concentration is circulated through the electrolytic reactor feed line, the mixing line, and the electrolytic reactor return line. In the mixing line, the solution sent from the cleaning device and the solution sent from the electrolytic reaction device are mixed at the upstream end and flow downstream. The mixing line is not particularly limited as long as the solution is mixed and flows downstream, and its configuration shape and the like are not particularly limited. For example, it can be constituted by piping. The solution sent from the cleaning apparatus has a reduced persulfuric acid concentration due to self-decomposition, and the solution contains a dissolved material such as a resist peeled from the material to be cleaned in the cleaning apparatus. On the other hand, the solution sent from the electrolytic reaction apparatus has a high persulfate concentration as persulfate ions are generated. When these solutions are mixed, the mixture is averaged higher than the concentration of the solution sent from the cleaning device and lower than the concentration of the solution sent from the electrolytic reactor according to the concentration and flow rate of both. It has a high persulfate concentration. In this mixing line, the dissolved resist or the like contained in the solution sent from the cleaning device is decomposed as it flows through the mixing line with persulfuric acid having an increased concentration.

  Moreover, when both solutions are mixed, the temperature of both is also averaged. In the cleaning apparatus, the dissolution rate of the resist into the persulfuric acid solution increases as the temperature of the persulfuric acid solution increases. However, if it exceeds 160 ° C., the self-decomposition rate of persulfuric acid becomes extremely high. Therefore, the temperature of the persulfuric acid solution as the cleaning liquid is desirably 120 to 150 ° C. In the present invention, although not essential, in order to heat the cleaning liquid to the above temperature, it is desirable to provide a heating device such as a heater, hot water, or steam. Therefore, normally, the solution sent from the cleaning device is at a high temperature.

  On the other hand, the electrolytic reaction apparatus differs from the cleaning apparatus in that the lower the solution temperature, the better the efficiency of producing persulfuric acid and the smaller the electrode wear. In the present invention, by separating the cleaning device and the electrolytic reaction device, the temperature of the solution electrolyzed in the electrolytic reaction device can be kept lower than the temperature of the cleaning liquid in the cleaning tank. In addition, the efficiency in the electrolytic reaction apparatus can be increased. For this reason, the solution electrolyzed by the electrolytic reaction apparatus can be cooled to an appropriate temperature by an appropriate cooling means. Examples of the cooling means include air coolers and water coolers. The appropriate temperature as the solution to be electrolyzed can be in the range of 10 to 90 ° C. When the temperature range is exceeded, the electrolysis efficiency decreases and the wear of the electrode also increases. On the other hand, if the temperature is lower than the above temperature, the heat energy for heating the cleaning bath temperature to an appropriate temperature becomes enormous, 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. Therefore, the solution sent from the electrolytic reaction apparatus is usually at a low temperature. Both the mixed solutions have a low temperature as a cleaning solution and a high temperature as a solution to be electrolyzed. The temperature of the solution flowing through the mixing line is further reduced by heat dissipation. When this solution further flows from the mixing line into the electrolytic reactor through the electrolytic reactor return line, no special cooling means is required if the temperature is reduced to a suitable temperature. On the other hand, it is desirable that the solution flowing from the mixing line to the cleaning device through the cleaning device return line is heated by a heating device so as to have an appropriate temperature.

  In addition, the dissolved resist contained in the cleaning solution is decomposed while the mixed solution flows through the mixing line. At this time, the temperature of the mixed solution is lower than that of the cleaning solution. Self-decomposition is suppressed, and the dissolved resist is reliably decomposed over a long time in the mixing line. In the mixing line, it is desirable that the liquid mixture passes through the mixing line while retaining a certain amount of time so that the resist melt and the like are sufficiently decomposed. However, since the resist decomposition time with persulfuric acid is within 20 minutes, the above passage time is preferably 20 minutes or less in consideration of downsizing of the cleaning efficiency apparatus. Further, as described above, it is desirable that a passage time of 5 minutes or longer is required in order to reliably decompose the dissolved matter. This is because, if the passage time is too short, the dissolved resist or the like flows into the electrolytic reaction device without being decomposed, and the electrode provided in the electrolytic reaction device is worn out. In addition, when the mixed solution flows through the mixing line, the flow rate is slow in the plug flow so that there is no drift of the resist dissolved material etc. in the mixing line and the residence time in the mixing line is secured. Is desirable.

  Further, the dissolution rate of the resist in the persulfuric acid solution increases as the sulfuric acid concentration increases. The sulfuric acid concentration as the cleaning liquid is preferably 8M or more, more preferably 12M or more. Therefore, it is desirable that the sulfuric acid concentration of the solution flowing through the entire system be in the above range.

  In addition, the said washing | cleaning apparatus makes a to-be-cleaned material and cleaning fluid contact, and peels and removes the contaminant on the to-be-cleaned material surface, The structure is not limited to a specific thing. For example, a cleaning tank may be provided, the cleaning liquid may be accommodated in the cleaning tank, and the material to be cleaned may be immersed, or the cleaning liquid may be sprayed onto the material to be cleaned as droplets.

  On the other hand, in an electrolytic reaction apparatus, electrolysis is performed by pairing an anode and a cathode in an electrolytic reaction tank. 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 platinum is eluted. On the other hand, the conductive diamond electrode can efficiently generate persulfate ions and has little electrode wear. Therefore, among the electrodes of the electrolytic reaction apparatus, at least the anode that generates sulfate ions is preferably composed of a conductive diamond electrode, and it is more desirable that both the anode and the cathode are composed of a conductive diamond electrode.

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. Production of persulfate ions from sulfate ions using a conductive diamond electrode has been reported for a current density of about 0.2 A / cm ² (Ch. Comninellis et al., Electrochemical and Solid- State Letters, Vol. 3 (2) 77-79 (2000), Patent Document 2), 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. is there. Therefore, a self-standing type conductive diamond electrode in which the substrate is removed after being deposited on the substrate is desirable.
The conductive diamond thin film is a conductive thin film that is doped with a predetermined amount of boron or nitrogen during the synthesis of the diamond thin film, and is generally boron-doped. If the doping amount is too small, 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 such that the current density on the surface of the conductive diamond electrode is 10 to 100,000 A / m ² , the sulfuric acid solution is parallel to the surface of the conductive diamond electrode, and the liquid flow rate is 10 to 10 It is desirable to perform the contact treatment at 000 m / h.

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

  As described above, according to the sulfuric acid recycling type cleaning system of the present invention, the cleaning apparatus for cleaning the material to be cleaned using the persulfuric acid solution as the cleaning liquid, and the solution used for cleaning are electrolyzed and included in the solution. An electrolytic reaction device that regenerates a persulfate solution by generating persulfate ions from sulfate ions, a cleaning device feed line that sends the solution from the cleaning device, a cleaning device return line that returns the solution to the cleaning device, and the electrolytic reaction An electrolytic reaction device feed line for sending the solution from the device, an electrolytic reaction device return line for returning the solution to the electrolytic reaction device, the cleaning device feed line and the electrolytic reaction device feed line merge at the upstream end, and the downstream end Since it is equipped with a mixing line that divides into the cleaning device return line and the electrolytic reactor return line, persulfuric acid is used to repeatedly use the sulfuric acid solution and enhance the peeling effect On the may be used to supply the cleaning device a part of regenerated by electrolytic reaction apparatus. In addition, efficient cleaning can be continued without requiring addition of a chemical solution such as hydrogen peroxide or ozone from the outside. In addition, since the solution from the cleaning device and the solution from the electrolytic reaction device are mixed and flowed in the mixing line, it is possible to proceed with the decomposition of the resist melt, etc., and the melt immediately flows into the electrolytic reaction device. Thus, the electrode is prevented from being worn. Further, by mixing the solution sent from the electrolytic reaction device with the solution sent from the cleaning device, the heat of both solutions can be directly transferred and energy loss can be reduced.

Below, one Embodiment of this invention is described based on FIG.
The sulfuric acid recycling type cleaning system of the present invention has a cleaning tank 1 as a cleaning device for cleaning a material to be cleaned. Connected to the washing tank 1 are a feed pipe 5 that is a washing apparatus feed line for sending the solution in the washing tank 1 and a return pipe 7 that is a washing apparatus return line for returning the solution into the washing tank 1. A liquid feed pump 6 is interposed in the return pipe 7. The feed pipe 5 is connected to the upstream end of the mixing pipe 20 which is a mixing line by a T-joint, and the return pipe 7 is also connected to the downstream end of the mixing pipe 20 by a T-joint, so that the solution in the washing apparatus Circulation is possible. The cleaning tank 1 is provided with a heater 2 for heating the cleaning liquid in the tank to 120 to 150 ° C. as a heating device, and ultrapure water is mixed when the cleaning liquid is prepared. Therefore, an ultrapure water supply line 8 is connected.

The sulfuric acid recycling type cleaning system of the present invention has an electrolytic reaction tank 10 as an electrolytic reaction device. The electrolytic reaction tank 10 includes a feed pipe 15 that is an electrolytic reaction apparatus feed line for sending the solution in the electrolytic reaction tank 10, and a return that is an electrolytic reaction apparatus return line for returning the solution into the electrolytic reaction tank 10. A pipe 17 is connected, and a liquid feed pump 16 is interposed in the return pipe 17. The feed pipe 15 is connected to the upstream end of the mixing pipe 20 by a T-shaped joint, and the return pipe 17 is connected to the downstream end of the mixing pipe 20 by a T-shaped joint so that the solution can be circulated in the electrolytic reaction tank 10. It has become.
In addition, it is desirable that at least the inner surfaces of the flow paths of the feed pipes 5 and 15 and the return pipes 7 and 17 are made of tetrafluoroethylene.

  In addition, an anode 11 and a cathode 12 are disposed in the electrolytic reaction tank 10, and a bipolar electrode 13 is disposed at a predetermined interval between the anode 11 and the cathode 12. The present invention is not bipolar, and may be provided with only an anode and a cathode as electrodes. A direct current power source 14 is connected to the anode 11 and the cathode 12, thereby enabling direct current electrolysis in the electrolytic reaction tank 10.

  In this embodiment, the anode, cathode, and bipolar electrode in each of the electrolytic reaction tanks are composed of conductive diamond electrodes. The conductive diamond electrode is produced by forming a diamond thin film in the form of 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. Preferably, after the thin film is formed, the substrate is removed to form a self-stand type.

Next, the operation of the sulfuric acid recycling type cleaning system having the above configuration will be described.
A sulfuric acid solution is accommodated in the washing tank 1 and ultrapure water is supplied and mixed at a predetermined mixing ratio from the ultrapure water supply line 8 to prepare a sulfuric acid solution having a sulfuric acid concentration of 8 to 15M. In the washing tank 1, the solution is circulated through the feed pipe 5, the mixing pipe 20, and the return pipe 7 by the liquid feed pump 6. Further, by operating the liquid feeding pump 16, a part of the solution flowing through the mixing tube 20 flows to the return tube 17, and the solution circulates through the electrolytic reaction tank 10, the feeding tube 15, and the mixing tube 20.

In the electrolytic reaction tank 10, when the anode 11 and the cathode 12 are energized by the DC power source 14, the bipolar electrode 13 is polarized, and the anode and the cathode appear at a predetermined interval. The solution sent to the electrolytic reaction tank 10 is passed between these electrodes. At this time, it is desirable to set the output of the liquid feed pump 16 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 surface of the conductive diamond electrode is 10 to 100,000 A / m ² .

  When the solution is energized in the electrolytic reaction tank 10, the sulfate ions in the solution undergo an oxidation reaction to generate persulfate ions to obtain a persulfate solution. This persulfuric acid solution is sent from the feed pipe 15 to the mixing pipe 20 and mixed with the solution sent from the washing tank 1 through the feed pipe 5. The solution whose persulfuric acid concentration is increased by this mixing passes through the mixing tube 20, and a part of the solution is sent to the washing tank 1 through the return tube 7. Thereby, a highly concentrated persulfuric acid solution is obtained in the washing tank 1. In the washing tank 1, although the persulfate ion concentration is reduced by autolysis, it is mixed with the high-concentration solution sent from the electrolytic reaction tank 10 by being sent from the feed pipe 5 to the mixing pipe 20, and as described above. As the solution having a higher concentration flows through the return pipe 7, the persulfate ion concentration is maintained.

  The persulfuric acid solution in the cleaning tank 1 is heated as a cleaning liquid by the heater 2 and maintained at 120 to 150 ° C. In order to start the cleaning of the semiconductor wafer that is the material to be cleaned in the cleaning tank 1, the semiconductor wafer is immersed in the cleaning tank 1. In the cleaning tank 1, a high oxidizing action is obtained by a cleaning action by concentrated sulfuric acid of high concentration and self-decomposition of persulfate ions, and most of the resist which is a contaminant on the semiconductor wafer is effectively stripped and removed. . The resist dissolved material moves into the cleaning solution and is decomposed by persulfuric acid. The solution in the cleaning tank 1 moves to the outside through the feed pipe 5. At this time, decomposition of the dissolved matter proceeds, and further mixing with a high-concentration persulfuric acid solution in the mixing tube 20 increases the oxidizing power, and the resist dissolved material is further decomposed while moving the mixing tube 20. The Persulfate concentration is averaged by mixing the solutions. The cleaning liquid that joins the mixing pipe 20 through the feed pipe 5 is heated to a high temperature (120 to 150 ° C.) by the heater 2 as described above. On the other hand, the solution that merges from the electrolytic reaction tank 10 through the feed pipe 15 is lowered to a temperature (10 to 90 ° C.) suitable for the electrolytic reaction tank, and the temperature is averaged by mixing both solutions. The inside of the mixing tube 20 is in a plug flow state by maintaining a low flow rate of 0.1 m / second or less, and the time during which the solution stays in the mixing tube 20 according to the flow rate determined by the liquid feed pumps 6 and 16. Passes almost constant.

Part of the solution that has passed through the mixing tube 20 is introduced into the cleaning tank 1 through the return tube 7. This solution has a high concentration of persulfuric acid due to merging with a high-concentration persulfuric acid solution, and the material to be cleaned can be continuously cleaned while being heated by the heater 2. On the other hand, a part of the solution that has passed through the mixing tube 20 is introduced into the electrolytic reaction tank 10 through the return tube 17. In the electrolytic reaction tank 10, persulfate ions are generated from the sulfate ions by energization through the electrodes, the persulfate concentration lowered by the self-decomposition is increased, and the persulfate solution is regenerated. The liquid is sent to.
After the semiconductor wafer cleaned by the cleaning tank 1 is immersed in the cleaning tank 1 for a predetermined time, the semiconductor wafer can be rinsed with ultrapure water or the like in the conventional manner.

By cleaning the semiconductor wafer with the sulfuric acid recycling type cleaning system, it is possible to regenerate the persulfuric acid solution by repeatedly using the persulfuric acid solution without requiring the addition of hydrogen peroxide or ozone. Washing can be continued.
Although the present invention has been described based on the above embodiment, the present invention is not limited to the description of the above embodiment, and can naturally be changed without departing from the scope of the present invention. .

  About 0.7 liters of sulfuric acid solution from the washing tank 1 containing 50 liters of 15M concentrated sulfuric acid in total using a pipe made of tetrafluoroethylene (feed pipe 5 + mixing pipe 20 + return pipe 7: inner diameter 18 mm, length 20 m) The cleaning liquid in the cleaning tank 1 was heated and maintained at 130 ° C. by the heater 2. A sulfuric acid solution containing persulfuric acid is mixed and mixed at the upstream end of the mixing tube 20 from the electrolytic reaction tank 10 through the feed tube 15 at a flow rate of about 0.3 liter / min. From 17, the solution was returned to the electrolytic reaction tank 10 at a flow rate of about 0.3 liter / min using the liquid feed pump 16. The length of the mixing tube 20 was 17 m.

In the electrolytic reaction vessel 10, ten conductive diamond electrodes 12 doped with boron on a Si substrate having a diameter of 15 cm and a thickness of 1 mm were incorporated. Effective anode area for electrolysis is 15dm ^2, by setting the current density 60A / dm ^2, and electrolysis at 40 ° C.. A direct current was supplied to the electrolytic reaction tank 10 by using a direct current power source 14.
As a pretreatment, 10 5-inch silicon wafers with a patterned resist of 100 nm that were not subjected to an ashing treatment were immersed in the cleaning tank 1 for 10 minutes to remove the resist. Finally, it was rinsed with ultrapure water and spin-dried.
When the organic residue was measured for the cleaned wafer using a wafer analyzer, the residue was about 100 to 200 pg / cm ² , and it was confirmed that a highly clean wafer could be obtained.
The same cleaning operation was repeated at 120 wafers / hr, and when organic residues were measured using a wafer analyzer after cleaning for a total of 8 hours, the residues were about 100 to 200 pg / cm ² , and changed from the initial cleaning. It was confirmed that a highly clean wafer could be obtained.

(Comparative Example 1)
50 liters of 15M concentrated sulfuric acid was placed in the washing tank 1 used in Example 1, and the entire sulfuric acid solution was heated and maintained at 130 ° C. by the heater 2.
Without operating the electrolytic reaction tank 10, 10 liters of hydrogen peroxide solution was added to this solution, and the solution was circulated only by the feed pipe 5, the mixing pipe 20, and the return pipe 7. Ten 5-inch silicon wafers with a 100 nm patterned resist that were not subjected to ashing treatment were immersed for 10 minutes to remove the resist. Finally, it was rinsed with ultrapure water and spin-dried. The resist removal effect on the wafer was good, and the sulfuric acid solution was colored light brown immediately after immersion, but became colorless and transparent in less than 10 minutes, and the TOC concentration became the detection limit.
When the organic residue was measured for the cleaned wafer using a wafer analyzer, the residue was about 100 to 200 pg / cm ² , and it was confirmed that a highly clean wafer could be obtained.
The same cleaning operation was repeated at 120 wafers / hr, and when the light brown color of the sulfuric acid solution disappeared, hydrogen peroxide solution was added repeatedly. Was measured, and the residue was 4,000 to 7,000 pg / cm ^2, and it was confirmed that the residue was at a clean level that could not proceed to the next step.

1 is an overall view showing an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Washing tank 2 Heater 5 Feeding pipe 6 Liquid feeding pump 7 Return pipe 10 Electrolytic reaction tank 11 Anode 12 Cathode 13 Bipolar electrode 14 DC power supply 15 Feeding pipe 16 Liquid feeding pump 17 Return pipe 20 Mixing pipe

Claims (7)

  A cleaning apparatus for cleaning a material to be cleaned using a persulfate solution as a cleaning solution, and an electrolytic reaction for regenerating the persulfate solution by electrolyzing the solution used for cleaning and generating persulfate ions from sulfate ions contained in the solution An apparatus, a cleaning device feed line through which the solution is sent from the cleaning device, a cleaning device return line for returning the solution to the cleaning device, an electrolytic reaction device feed line through which the solution is sent from the electrolytic reaction device, and the electrolytic reaction device An electrolytic reaction device return line for returning the solution to a mixing line, and a mixing line in which the cleaning device feed line and the electrolytic reaction device feed line merge at the upstream end and branch to the washing device return line and the electrolytic reaction device return line at the downstream end And a sulfuric acid recycling type cleaning system.   The sulfuric acid recycle type cleaning system according to claim 1, wherein the flow of the solution in the mixing line is a plug flow having a flow rate of 0.1 m / sec or less.   The sulfuric acid recycle type cleaning system according to claim 1 or 2, wherein the time for which the solution flows through the mixing line is 20 minutes or less.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 3, further comprising a heating device that heats the cleaning liquid to 120 to 150 ° C.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 4, wherein the temperature of the electrolytically reacted solution is in the range of 10 to 90 ° C.   The sulfuric acid recycle type cleaning system according to claim 1, wherein the sulfuric acid concentration of the solution is 8 M or more.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 6, wherein a conductive diamond electrode is used for at least an anode among electrodes used in an electrolytic reaction apparatus.

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