JP4407557B2 - Sulfuric acid recycling cleaning method and sulfuric acid recycling cleaning system - Google Patents

Description

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

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 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 these methods, there is a limit to the concentration of persulfuric acid produced, which leads to the limit of the cleaning effect.

  In most cleaning methods including SPM, the cleaning process is performed only with a preset cleaning time and without any cleaning factor being controlled. For example, in the case of SPM, every time hydrogen peroxide solution is added, the concentration of sulfuric acid decreases, and the cleaning ability decreases. Therefore, the required cleaning time in a state where the ability is low is a standard. Therefore, when the solution is new, it takes more cleaning time than necessary, and there is a problem that the efficiency is poor.

  The present invention has been made against the background of the above circumstances, and by reusing persulfate ions from an aqueous solution of sulfuric acid by electrochemical action while repeatedly using sulfuric acid, the persulfate ions are recycled to greatly increase the amount of sulfuric acid used. Providing a sulfuric acid recycle type cleaning method and sulfuric acid recycle type cleaning system that can continuously obtain good cleaning action by reducing the amount of water to be used, and can accurately grasp the cleaning state and perform an efficient cleaning process. The purpose is to do.

That is, among the sulfuric acid recycling type cleaning methods of the present invention, the invention according to claim 1 is included in the solution by cleaning the material to be cleaned using a persulfuric acid solution as a cleaning liquid and electrolyzing the solution used for the cleaning. playing the persulfate solution to produce persulfate ions from sulfate ions donate as the cleaning solution, while continuously performed and the electrolyte reacting with the cleaning by the cleaning, deposit of the object to be cleaned material the Along with the shift to the solution, captures the concentration of the deposit in the solution increases as the decrease in conductivity of the solution, determining the cleaning degree of the object to be cleaned on the basis of a change of the conductivity It is characterized by that.

  The sulfuric acid recycling type cleaning method according to claim 2 is characterized in that, in the invention according to claim 1, the change in conductivity is detected by measuring resistivity or conductivity of the solution. .

  The sulfuric acid recycle type cleaning method according to claim 3 is the invention according to claim 1, wherein the change in conductivity is a voltage between electrodes during constant current electrolysis or current between electrodes during constant voltage electrolysis in the electrolysis. It is detected by measuring.

  According to a fourth aspect of the present invention, there is provided the sulfuric acid recycling type cleaning method according to any one of the first to third aspects, wherein the determination of the degree of cleaning is performed in a predetermined manner because the conductivity of the solution decreases with cleaning. After reaching the electrical conductivity, it rises and reaches a predetermined electrical conductivity, so that it is determined that the cleaning is finished.

  According to a fifth aspect of the present invention, there is provided a sulfuric acid recycle type cleaning method according to the third aspect of the present invention, wherein the determination of the degree of cleaning is performed by increasing a voltage between electrodes during constant current electrolysis in the electrolysis with a predetermined value. After reaching the value, it is determined that the cleaning is finished by lowering and reaching a predetermined value.

  According to a sixth aspect of the present invention, there is provided the sulfuric acid recycling type cleaning method according to the third aspect of the present invention, wherein the determination of the degree of cleaning is based on a predetermined value due to a decrease in inter-electrode current during constant voltage electrolysis in the electrolysis. After reaching this value, it rises and reaches a predetermined value to determine that the cleaning is finished.

The invention of the sulfuric acid recycling type cleaning system according to claim 7 includes a cleaning device for cleaning a material to be cleaned using a persulfuric acid solution as a cleaning liquid, and an electrolysis of the solution used for the cleaning to prevent excess from sulfate ions contained in the solution. An electrolytic reaction device that regenerates a persulfuric acid solution by generating sulfate ions, a circulation line that circulates the persulfuric acid solution between the cleaning device and the electrolytic reaction device, and deposits of the material to be cleaned by the cleaning And a conductivity measuring instrument that measures the conductivity of the solution that changes as the concentration of the deposit in the solution increases as the solution moves into the solution .

  An invention of a sulfuric acid recycle type cleaning system according to claim 8 is characterized in that, in the invention according to claim 7, the conductivity measuring device measures the resistivity or conductivity of the solution.

  The invention of the sulfuric acid recycling type cleaning system according to claim 9 is the invention according to claim 7, wherein the conductivity measuring device is a voltage between electrodes during constant-current electrolysis or an electrode between constant-voltage electrolysis in an electrolytic reaction device. The current is measured.

  The invention of the sulfuric acid recycle type cleaning system according to claim 10 controls the cleaning process of the material to be cleaned based on the measurement result by the conductivity measuring instrument in the invention according to any one of claims 7 to 9. A cleaning control unit is provided.

  The invention of the sulfuric acid recycle type cleaning system according to claim 11 is the invention according to claim 10, wherein the cleaning treatment step includes the transfer of the material to be cleaned to the cleaning device, the contact between the material to be cleaned and the cleaning liquid, and the cleaning device. Including a process of carrying out the material to be cleaned.

  The invention of the sulfuric acid recycle type cleaning system according to claim 12 is the invention according to claim 10 or 11, wherein the cleaning control unit reaches a predetermined conductivity as the conductivity of the solution decreases with cleaning. Thereafter, it rises and reaches a predetermined conductivity, it is determined that the cleaning is completed, and a command signal for discharging the material to be cleaned is output from the cleaning device.

  The invention of the sulfuric acid recycling type cleaning system according to claim 13 is the invention according to claim 10 or 11, wherein the cleaning controller increases the voltage between the electrodes during constant current electrolysis in the electrolysis as the cleaning proceeds. After reaching the value, it descends and reaches a predetermined value to determine that the cleaning is finished, and outputs a command signal for discharging the material to be cleaned from the cleaning device.

  The invention of the sulfuric acid recycling type cleaning system according to claim 14 is the invention according to claim 10 or 11, wherein the cleaning control unit is configured to reduce the current between electrodes during constant voltage electrolysis in the electrolysis as the cleaning proceeds. After reaching the value, it rises and reaches a predetermined value, and it is determined that the cleaning is completed, and a command signal for discharging the material to be cleaned is output from the cleaning device.

  A sulfuric acid recycling type cleaning system according to a fifteenth aspect of the present invention is the invention according to any one of the seventh to fourteenth aspects, wherein the electrode in the electrolytic reaction apparatus is a conductive diamond electrode.

That is, according to the present invention, persulfate ions in the cleaning liquid self-decompose and generate oxidizing power, and contaminants and the like of the material to be cleaned 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 subjected to electrolytic treatment by being sent to an electrolytic reactor through a circulation line. In the electrolytic treatment, the anode and the cathode are immersed in the persulfuric acid 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 sufficiently high. Regenerated to persulfate solution. The regenerated persulfuric acid solution is supplied to a cleaning device through a circulation line and is subjected to a cleaning process. In the same manner as described above, the material to be cleaned is effectively peeled and cleaned with high concentration of persulfuric acid. Persulfuric acid can be continuously circulated between the cleaning device (cleaning treatment) and the electrolytic reaction device (electrolytic processing), 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.
Furthermore, the degree of cleaning of the object to be cleaned is determined by observing the change in conductivity of the solution used for cleaning, and by taking this cleaning degree into account, reliable cleaning is performed and useless cleaning time is reduced. This eliminates the need for efficient cleaning.

  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 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, when the temperature is lower than the above temperature, the heat energy for heating the cleaning tank to a 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.
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, heat exchange is performed between the persulfuric acid solution that is relatively heated and sent from the cleaning device to the electrolytic reaction device, and the persulfuric acid solution that is relatively lowered in temperature and returned from the electrolytic reaction device to the cleaning device. Then, the temperature of the feed liquid having a high temperature is reduced by heat being removed by heat exchange, and a temperature adjustment desirable as an electrolysis solution of the electrolytic reaction apparatus is performed. In addition, the return 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 the above system, the concentration of sulfuric acid in the persulfuric acid solution serving as the cleaning liquid greatly affects the efficiency of persulfuric acid generation by electrolysis and the effect of removing organic substances such as resist from the electronic material substrate. When the sulfuric acid concentration is about 7 to 10M, the efficiency of persulfuric acid generation by electrolysis increases, but the peeling / dissolving effect of organic substances such as resist decreases as the sulfuric acid concentration decreases. Therefore, the inventors have repeated various experiments and found that a sulfuric acid concentration in the range of 8M to 18M can be applied as an appropriate cleaning solution. 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 the anode of the electrolytic reaction apparatus of the present invention, there is a problem that persulfate ions cannot be produced efficiently and platinum is eluted. On the other hand, the conductive diamond electrode can efficiently generate persulfate ions and has little electrode wear. Therefore, among the electrodes of the electrolytic reaction apparatus, at least the anode that generates persulfate ions is preferably composed of a conductive diamond electrode, and it is more desirable that both the anode and the cathode be 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. 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.

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. Cominellis et al., Electrochemical and Solid-State). Letters, Vol. 3 (2) 77-79 (2000), Patent Document 2). 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-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, 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 passed in a direction parallel to the surface of the conductive diamond electrode. It is desirable to perform the contact treatment at a linear velocity of 1 to 10,000 m / hr.

  The cleaning apparatus may be any of a single wafer type, a batch type, an immersion type, a droplet type, and the like, and is not limited to a specific type in the present invention. In short, any material that can clean the contaminants of the material to be cleaned by bringing the cleaning liquid into contact with the material to be cleaned may be used. In the cleaning apparatus, TOC is generated in the cleaning liquid along with the separation and dissolution of contaminants such as resist during cleaning of the electronic material substrate. At this time, since it is necessary to efficiently remove the TOC of the cleaning liquid and sufficiently prevent the organic contaminants from reattaching to the electronic substrate material, the excess of the TOC increase rate [g / l / hr] The electrolysis conditions are preferably set so that the sulfuric acid production rate [g / l / hr] is 10 to 500 times. This balances the consumption and generation of persulfuric acid, and allows efficient cleaning and efficient electrolytic treatment. For the same reason, it is more desirable to set the lower limit to 20 and the upper limit to 300.

Since persulfuric acid has a high oxidation resolution, it has a high effect on the removal of organic substances from the electric substrate material.
However, when the concentration of persulfuric acid in the cleaning liquid is low, incompletely decomposed organic substances and the like are reattached to the electronic substrate material, resulting in a decrease in cleaning effect and adversely affecting the next process. On the other hand, if the persulfuric acid concentration is too high, most of the persulfuric acid generated electrolytically due to its chemical characteristics is self-decomposed, resulting in energy loss. In particular, after cleaning the wafer, the resist dissolves in the sulfuric acid solution. It is difficult to measure the concentration with a total organic carbon concentration meter (TOC meter) because the solution is strongly acidic, and there is no other good analysis technique. Therefore, it is necessary to wait for the wafer cleaning interval during batch cleaning until the resist is decomposed and a sufficient persulfuric acid concentration is recovered for a certain period of time. However, this often depends on empirical intuition. Therefore, in the present invention, the principle that the conductivity of the solution changes when the resist is dissolved in the sulfuric acid solution is used to capture the change in the concentration of the resist in the solution as the change in conductivity. Therefore, the degree of cleaning of the material to be cleaned can be known by observing the change in conductivity.

For example, at the initial stage of cleaning, the resist or the like attached to the object to be cleaned is peeled off and removed, and the concentration of the resist or the like in the solution increases by moving into the solution. Usually, organic substances such as resists do not have conductivity, so that the conductivity of the solution decreases as the resist concentration in the solution increases. As the cleaning progresses, the amount of dissolved matter transferred from the material to be cleaned into the solution decreases, while the dissolved matter in the solution is decomposed by persulfuric acid and gradually decreases in concentration. This decrease in concentration appears as an increase in conductivity. Therefore, it can be determined that the cleaning has been completed because the conductivity has increased to a certain level after the conductivity has decreased.
Therefore, by observing the change in conductivity, it is possible to quickly and easily know the degree of cleaning of the material to be cleaned.

The change in conductivity can be grasped by a measuring instrument that can know the conductivity. The change in conductivity can be known by measuring the resistivity and conductivity of the solution, and these measurements can be performed by a resistivity measuring device and a conductivity measuring device. The measurement location such as resistivity is not particularly limited, and the measurement can be performed at an appropriate place in the circulation line, the cleaning device, or the electrolytic reaction device.
Further, the change in conductivity can be grasped by measuring the voltage between the electrodes during constant current electrolysis and the current between the electrodes during constant voltage electrolysis. These measurements can be performed with a voltmeter or an ammeter, and can be measured with an electrolytic reaction apparatus.
The above-described device for measuring conductivity is not limited to a specific one as the present invention, and a known device can be used.

  The result of measuring the change in conductivity may be that the operator operates the system by knowing this, and in this case, the operator is notified of the measurement result by displaying on the display unit or generating sound. Is required. In addition, a control unit that determines the degree of cleaning from the change in conductivity can be provided, and a display that notifies the end can be performed by the cleaning end determination by the control unit. In the control unit, for example, the change in conductivity and the degree of cleaning are associated in advance and stored as data in a storage unit such as a nonvolatile memory or a disk, and the degree of cleaning is determined by reading out the related data based on the measurement result. Can be determined.

In the control unit, the cleaning process can be controlled on the basis of the change in conductivity, with regard to the loading / unloading of the cleaning material and the contact between the cleaning liquid and the cleaning material. For example, it is possible to determine whether to end cleaning and output a command signal for discharging the material to be cleaned from the cleaning device based on the determination. The signal may be used as a notification to the operator, or may be used to control the cleaning process. For example, when a device for carrying in / out a material to be cleaned is provided in / out of the cleaning device, the carry-in / out device can be controlled by the command signal to perform an operation for carrying out the material to be cleaned from the cleaning device. Further, in addition to this, it is also possible to perform an operation of transporting a new material to be cleaned and carrying it into the cleaning device. In addition to the above control, the control unit can also control the entire system to control the on / off of the liquid feed pump, the opening / closing of the valve, the on / off of the power supply of the electrolytic reaction apparatus, and the like. The control unit can be configured by, or mainly configured by, a CPU and a program for operating the CPU, for example.
With the above, it is possible to efficiently clean the material to be cleaned such as a wafer, and to improve the yield of the material to be cleaned such as a wafer. Furthermore, since the degree of cleaning can be accurately grasped, the number of sheets to be cleaned per unit time can be increased.

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 method of the present invention, the material to be cleaned is cleaned using a persulfuric acid solution as a cleaning liquid, and the solution used for the cleaning is electrolyzed, thereby sulfate ions contained in the solution. A persulfate ion is generated from the solution to regenerate the persulfate solution, which is provided as the cleaning liquid, and the object to be cleaned is based on the change in conductivity of the solution by the cleaning while continuously performing the cleaning and the electrolytic reaction. Therefore, it is possible to recycle the persulfuric acid solution for reusing the sulfuric acid solution on-site by the electrolytic reactor and use it for cleaning. Efficient cleaning can be continued without the need for adding chemicals such as ozone. In addition, the degree of cleaning of the material to be cleaned can be regarded as a change in the conductivity of the solution, and the cleaning can be performed efficiently. It is also possible to maintain high cleanliness by ensuring cleaning. Furthermore, since the degree of cleaning can be accurately grasped, the number of sheets to be cleaned per unit time can be increased.

  In addition, according to the sulfuric acid recycling type cleaning system of the present invention, a persulfate solution is generated from a sulfate ion contained in the solution by a cleaning apparatus for cleaning a material to be cleaned using a persulfuric acid solution as a cleaning liquid, and persulfuric acid. The above-mentioned operation is provided with an electrolytic reaction device for regenerating the solution, a circulation line for circulating the persulfuric acid solution between the cleaning device and the electrolytic reaction device, and a conductivity measuring device for measuring the conductivity of the solution. Can be definitely obtained.

Next, an embodiment of the present invention will be described with reference to FIGS.
The cleaning tank 1 corresponding to the cleaning apparatus of the present invention is provided with a heater 2 as a heating apparatus for heating the cleaning liquid in the tank, and the concentration of sulfuric acid is adjusted by introducing ultrapure water into the tank. An ultrapure water supply line 3 is connected. Further, above the cleaning tank 1, a wafer carry-in / out device 25 for carrying in / out the semiconductor wafer 20 as a material to be cleaned to / from the cleaning tank 1 is disposed.

  A circulation line feed pipe 4 is connected to the drainage section of the cleaning tank 1, and a return pipe 6 of the circulation line is connected to the water inlet section of the cleaning tank 1. The feed pipe 4 is provided with a feed pump 5 for feeding a persulfuric acid solution. On the downstream side of the liquid feed pump 5, a heat exchanger 7 that performs heat exchange is interposed between the feed pipe 4 and the return pipe 6. The downstream end of the feed pipe 4 is connected to the water inlet side of the electrolytic reaction tank 10a.

  In the electrolytic reaction tank 10a, an anode 11a and a cathode 12a are arranged, and further, bipolar electrodes 13a ... 13a are arranged at a predetermined interval between the anode 11a and the cathode 12a. 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 14 is connected to the anode 11a and the cathode 12a, thereby enabling DC electrolysis in the electrolytic reaction tank 10a.

The electrolytic reaction tank 10a is configured so that the solution passes between the electrodes. A connecting pipe 15 is connected to the water discharge side of the electrolytic reaction tank 10a, and the other end is the water inlet side of the electrolytic reaction tank 10b. It is connected to the.
The electrolytic reaction tank 10b has the same configuration as that of the electrolytic reaction tank 10a. The anode 11b and the cathode 12b are arranged, and the bipolar electrode 13b... Has a predetermined interval between the anode 11b and the cathode 12b. 13b is arranged so that the solution passes between the electrodes. A DC power supply 14 common to the electrolytic reaction tank 10a is connected to the anode 11b and the cathode 12b. As a result, direct current electrolysis is also possible in the electrolytic reaction tank 10b.

  In this embodiment, the DC power source 14 is provided with a constant current device (not shown), and electrolysis with a constant current is possible. In addition, a voltmeter 16 is connected as a conductivity measuring device in parallel with the DC power source 14, thereby enabling measurement of the voltage between the anode 11 a and the cathode 12 a and between the anode 11 b and the cathode 12 b. The measurement result of the voltmeter 16 is output to the control unit 17 that functions as a cleaning control unit. The control unit 17 includes a CPU, a program that operates the CPU, and a memory that stores determination data for determining the end of cleaning. The control unit 17 is configured to control the wafer carry-in / out device 25. The determination data is a data group in which voltage data and cleaning degree data are associated with each other.

In this embodiment, the electrodes 11a, 12a, 13a, 11b, 12b, and 13b are composed of conductive diamond electrodes. The conductive diamond electrode is manufactured by forming a diamond thin film on a substrate and doping boron in a range of preferably 50 to 20,000 ppm with respect to the carbon content of the diamond thin film. Alternatively, a self-stand type may be used by removing the substrate after forming the thin film.
A return pipe 6 is connected to the water discharge side of the electrolytic reaction tank 10b. That is, the electrolytic reaction apparatus is constituted by the electrolytic reaction tanks 10a and 10b, the DC power supply 14 and the connecting pipe 15 connected in series.

Next, the operation of the sulfuric acid recycling type cleaning system having the above configuration will be described.
The washing tank 1 contains sulfuric acid, and ultrapure water is mixed into the washing tank 1 at a predetermined volume ratio from the ultrapure water supply line 3 to obtain a sulfuric acid solution having a sulfuric acid concentration of 10 to 18M. This is sequentially fed to the electrolytic reaction tank 10a by the liquid feed pump 5. In the electrolytic reaction tank 10a, when a constant current is supplied to the anode 11a and the cathode 12a by the DC power supply 14, the bipolar electrodes 13a... 13a are polarized, and the anode and the cathode appear at predetermined intervals. The solution sent to the electrolytic reaction tank 10a is passed between these electrodes. 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 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 10a, the sulfate ions in the solution undergo an oxidation reaction to generate persulfate ions, thereby obtaining a high concentration persulfate solution. This persulfuric acid solution is further sent from the connecting pipe 15 to the electrolytic reaction tank 10b, and is energized by the DC power source 14 in the same manner as the electrolytic reaction tank 10a to generate persulfate ions. The persulfuric acid solution having a high concentration in this way is sent to the washing tank 1 through the return pipe 6. The persulfuric acid solution to be fed passes through the heat exchanger 7, where the heat is exchanged with the solution in the feeding tube 4 fed from the washing tank 1 toward the electrolytic reaction tank 10a, and the temperature rises. . This persulfuric acid solution is fed as a cleaning liquid to the cleaning tank 1 side and heated to 100 to 150 ° C. by the heater 2.

  A predetermined number of semiconductor wafers 20 are held in the wafer carry-in / out device 25, and the wafer carry-in / out device 25 is operated to carry the semiconductor wafer 20 into the cleaning tank 1 in which the cleaning liquid is accommodated to be used as the cleaning liquid. Immerse. In the cleaning tank 1, the surface of the semiconductor wafer 20 is cleaned with the cleaning liquid, and the resist and the like are peeled off and removed. The removed resist is dissolved in the cleaning solution. This lysate is gradually decomposed by the persulfuric acid in the cleaning solution. After cleaning the semiconductor wafer 20, the cleaning liquid is discharged to the feed tube 4 together with the dissolved resist. In the feed pipe 4, the persulfuric acid solution is fed to the electrolytic reaction tank 10 a by the liquid feed pump 5. At this time, heat exchange with the return pipe 6 is performed by the heat exchanger 7 to lower the temperature of the persulfuric acid solution, and the temperature is gradually lowered by natural cooling, which is suitable for electrolytic reaction from 10 ° C. to 90 ° C. The temperature is within the range of. In addition, when it is desired to reliably lower the temperature, a cooling means for forcibly cooling the persulfuric acid solution directed to the electrolytic reaction tank can be provided. When the liquid is fed through the feed pipe 4, decomposition of the resist dissolved material peeled and removed in the cleaning tank 1 also proceeds.

  The persulfuric acid solution is continuously sent from the electrolytic reaction tank 10a to the electrolytic reaction tank 10b, and the persulfate ion concentration is reduced by electrolysis to generate persulfate ions from the sulfate ions. Perform playback. After that, it is returned to the cleaning tank 1 through the return pipe 6 in the same manner as described above and used as a cleaning liquid, and cleaning is continued.

When starting the cleaning, as shown in FIG. 2, the voltage between the anode and the cathode is started by the voltmeter 16 as a procedure. The measurement result of the voltmeter 16 is output to the control unit 17, and the control unit 17 monitors the change in the measurement voltage. When it is confirmed that the voltage has increased to a certain level, it is determined that the resist dissolved matter in the solution has increased due to the cleaning. This is because when the resist dissolved matter increases in the solution due to the peeling of the resist from the semiconductor wafer 20, the resistivity of the solution increases, and in order to maintain a constant current, an operation of increasing the voltage by the DC power source 14 is performed. It is. At this time, it is observed whether or not a predetermined value has been reached by shifting to a voltage rising state. The predetermined value is stored in the control unit 17. After the voltage rise, the voltage change is further monitored, and it is observed whether or not the voltage has fallen to a predetermined value. The predetermined value is also set in advance as a target value for completion of cleaning and stored in the control unit 17. When it is confirmed that the measured voltage has reached the predetermined value, the control unit 17 determines the end of cleaning and controls the loading / unloading of the semiconductor wafer 20. That is, the wafer carry-in / out device 25 is controlled to carry out the semiconductor wafer 20 from the cleaning tank 1. The semiconductor wafer 20 can be rinsed using ultrapure water as in the prior art. Further, when the cleaning is continued, a new semiconductor wafer can be carried in and cleaning can be performed.
By cleaning the semiconductor wafer with the sulfuric acid recycling type cleaning system, it is possible to recycle the persulfuric acid solution by repeatedly using the sulfuric acid solution without requiring the addition of hydrogen peroxide or ozone. It is possible to continue, and the end of the cleaning can be efficiently performed by grasping the appropriate time.

In the above embodiment, constant current electrolysis is performed, and the voltage between electrodes in the electrolytic reaction tank is measured to observe the change in conductivity. In the present invention, for example, in the case of performing constant voltage electrolysis, as shown in FIG. 3, the interelectrode current in the electrolytic reaction tanks 10a and 10b is measured by an ammeter 18 to observe the change in conductivity. It may be a thing. In the measurement of the interelectrode current, the current value decreases as the resist melt increases, and the current value increases as the resist melt decreases.
In addition, as shown in FIG. 4, a conductivity meter or a resistivity meter 19 for measuring conductivity and resistivity is disposed at an appropriate position with respect to the solution circulating between the cleaning device and the electrolytic reaction device, thereby providing conductivity. It is good also as what observes a change of. In the measurement of conductivity, the conductivity decreases as the resist dissolution increases, and the conductivity increases as the resist dissolution decreases. In the resistivity measurement, the resist dissolution increases. Along with this, the resistivity increases, and the resistivity decreases as the resist melt decreases.
As mentioned above, although this invention was demonstrated based on the said embodiment, this invention is not limited to the content demonstrated by the said embodiment, In the range of this invention, it can change suitably.

Using the sulfuric acid recycle type cleaning system shown in Embodiment 1, a high concentration sulfuric acid solution was prepared in a cleaning apparatus at a ratio of 40 liters of 98% concentrated sulfuric acid and 10 liters of ultrapure water. In the electrolytic reaction apparatus, two electrolytic reaction tanks 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. Electrolysis was performed at a current density of 30 A / dm ² , and it was confirmed that the persulfuric acid concentration in the cleaning apparatus was 3 g / l. The cleaning target was a 5-inch silicon wafer with a resist, and the cleaning system was operated at a cleaning temperature of 130 ° C. and 50 wafers / batch. When the wafer was carried into the cleaning device, the reading of the voltmeter connected in parallel to the electrolytic reaction device rose by 4 V / vessel, but returned to the original voltage value within 7 minutes. This signal was immediately transmitted to the control unit, and the next 50 wafers were loaded into the cleaning apparatus at 7.5 minutes. This process was performed continuously for 3 hours, and 1200 clean wafers could be obtained.

  FIG. 5 shows the result of measuring the voltage for 10 conductive diamond electrodes in advance and measuring the TOC concentration off-line at that time, and there is a good correlation between the TOC and the voltage. Relationship is recognized. In consideration of this, if the TOC is 10 mg / liter or less (preferably 5 mg / liter or less), that is, if the voltage is 0.1 V / 10 or less (preferably 0.03 V / 10 or less), the resist concentration is increased. It is possible to perform a process of raising the wafer by judging that the level has sufficiently lowered and carrying in the next wafer.

(Comparative example)
Using the same cleaning liquid and cleaning system as in Example 1, the cleaning system was operated at 50 sheets / batch without monitoring the resist concentration. In order to wait until the resist concentration in the sulfuric acid solution was sufficiently lowered, this treatment was performed continuously for 3 hours with the interval between batches set to 10 minutes. As a result, only 900 wafers could be cleaned.

(Comparative Example 2)
Using the same cleaning liquid and cleaning system as in Example 1, the cleaning system was operated at 50 sheets / batch without monitoring the resist concentration. After cleaning, the sulfuric acid solution became transparent in 6 minutes. As a result of performing this treatment continuously for 3 hours with an interval between batches of 6 minutes, 1,500 wafers could be cleaned. In many cases, only about 20 to 30% of wafers can be transferred to the next process.

It is the schematic which shows one Embodiment of the sulfuric acid recycle type cleaning system of this invention. Similarly, it is a flowchart showing a procedure for estimating the degree of cleaning and ending cleaning. It is the schematic which shows embodiment changed similarly. It is the schematic which shows the embodiment which changed similarly similarly. It is a graph which shows the correlation of the voltage between electrodes, and TOC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Washing tank 2 Heater 4 Feeding pipe 5 Feeding pump 6 Return pipe 7 Heat exchanger 10a Electrolytic reaction tank 11a Anode 12a Cathode 13a Bipolar electrode 14 DC power supply 15 Connecting pipe 16 Voltmeter 17 Control part 18 Ammeter 19 Conductivity meter or Resistivity meter 20 Semiconductor wafer 25 Wafer loading / unloading device

Claims (15)

The material to be cleaned is washed with a persulfate solution as a washing liquid, and the solution used for washing is electrolyzed to generate persulfate ions from the sulfate ions contained in the solution to regenerate the persulfuric acid solution as the washing liquid. The concentration of the deposit in the solution increases as the deposit of the material to be cleaned moves into the solution by the cleaning while continuously performing the cleaning and the electrolytic reaction. wherein regarded as a decrease in conductivity of the solution, sulfuric acid recycling type cleaning method characterized by determining the cleaning degree of the object to be cleaned on the basis of a change of the conductivity to be.   The sulfuric acid recycle type cleaning method according to claim 1, wherein the change in conductivity is detected by measuring a resistivity or conductivity of the solution.   The sulfuric acid recycle type cleaning according to claim 1, wherein the change in conductivity is detected by measuring a voltage between electrodes during constant current electrolysis or a current between electrodes during constant voltage electrolysis in the electrolysis. Method.   The determination of the degree of cleaning is performed as a determination that the cleaning is finished by increasing and reaching a predetermined conductivity after the conductivity of the solution decreases and reaches a predetermined conductivity with the cleaning. The sulfuric acid recycle type cleaning method according to any one of claims 1 to 3.   The determination of the degree of cleaning is performed by determining that the cleaning is finished when the voltage between the electrodes during constant-current electrolysis in the electrolysis increases with the cleaning and reaches a predetermined value and then decreases and reaches a predetermined value. The sulfuric acid recycle type cleaning method according to claim 3, wherein   The determination of the degree of cleaning is performed by determining that the cleaning is finished when the current between the electrodes during constant voltage electrolysis in the electrolysis decreases and reaches a predetermined value as the cleaning increases and then reaches a predetermined value. The sulfuric acid recycle type cleaning method according to claim 3, wherein A cleaning apparatus for cleaning a material to be cleaned using a persulfuric acid solution as a cleaning liquid, and an electrolytic reaction apparatus for regenerating the persulfuric acid solution by electrolyzing the solution used for cleaning to generate persulfate ions from the sulfate ions contained in the solution And a circulation line that circulates the persulfuric acid solution between the cleaning device and the electrolytic reaction device, and the deposits of the material to be cleaned move into the solution by the cleaning, A sulfuric acid recycle type cleaning system comprising: a conductivity measuring device for measuring conductivity of the solution that changes as the concentration of the deposit increases .   8. The sulfuric acid recycle type cleaning system according to claim 7, wherein the conductivity measuring device measures the resistivity or conductivity of the solution.   The sulfuric acid recycle type cleaning according to claim 7, wherein the conductivity measuring device measures a voltage between electrodes during constant-current electrolysis in an electrolytic reaction apparatus or a current between electrodes during constant-voltage electrolysis. system.   The sulfuric acid recycle type cleaning system according to any one of claims 7 to 9, further comprising a cleaning control unit that controls a cleaning process step of a material to be cleaned based on a measurement result by the conductivity measuring instrument.   11. The sulfuric acid recycling type according to claim 10, wherein the cleaning process includes a process of transporting the material to be cleaned to the cleaning device, contacting the material to be cleaned with the cleaning liquid, and carrying out the material to be cleaned from the cleaning device. Cleaning system.   The cleaning control unit determines that the cleaning is finished when the conductivity of the solution decreases and reaches a predetermined conductivity as a result of cleaning, and then increases and reaches a predetermined conductivity. The sulfuric acid recycle type cleaning system according to claim 10 or 11, wherein a command signal for discharging the cleaning material is output.   The cleaning control unit determines that the cleaning ends when the voltage between the electrodes at the time of constant current electrolysis in the electrolysis increases and reaches a predetermined value along with cleaning, and then decreases and reaches a predetermined value. 12. The sulfuric acid recycling type cleaning system according to claim 10 or 11, wherein a command signal for discharging the material to be cleaned is output from the sulfuric acid recycling type.   The cleaning control unit determines that the cleaning ends when the current between the electrodes during constant voltage electrolysis in the electrolysis decreases and reaches a predetermined value along with cleaning, and then increases and reaches a predetermined value. 12. The sulfuric acid recycling type cleaning system according to claim 10 or 11, wherein a command signal for discharging the material to be cleaned is output from the sulfuric acid recycling type.   The sulfuric acid recycle type cleaning system according to claim 7, wherein at least an anode of the electrode in the electrolytic reaction apparatus is a conductive diamond electrode.

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