JP2007096058A - Washing system and washing method for sulfuric acid recycling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a washing system which uses persulfuric acid ions, the washing system being capable of efficient and secure washing while improving washing effect by making persulfuric acid ion density sufficiently high. <P>SOLUTION: The washing system is equipped with a washing device (washing tanks 1 and 2, a liquid spray nozzle liquid spray nozzle 2) which washes a washed material by using a persulfuric-acid-ion containing solution 16 as washing liquid, an electrolytic reaction device (electrolytic reaction tanks 20 and 25, and a DC power source 22) which generates persulfuric acid ions from sulfuric acid ions contained in the solution through electrolytic reaction to manufacture the persulfuric-acid-ion containing solution, a circulation line (return pipes 10a and 10b and feed pipes 11a and 11b) which circulates the persulfuric-acid-ion containing solution between the washing device and electrolytic reaction device, and a washing surface inspection device (a light emission and reception part 27 and a controller 28) which inspects a washed surface of the washed material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sulfuric acid recycling type cleaning system that electrolyzes and repeatedly uses a cleaning solution when cleaning and stripping contaminants attached to a silicon wafer and the like or unnecessary resist with a persulfate ion-containing solution having a high stripping effect. The present invention relates to a sulfuric acid recycling type cleaning method.

  The wafer cleaning technique in the VLSI manufacturing process is a process for peeling and cleaning resist residues, fine particles, metals, natural oxide films, etc., and a mixed solution (SPM) of concentrated sulfuric acid and hydrogen peroxide is used. It is known that the cleaning effect by SPM is due to the high oxidation resolution of persulfate ions generated by oxidizing hydrogen peroxide with sulfuric acid. As a method for generating persulfate ions, 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 cell to obtain persulfate ion-dissolved water and used for washing (Patent Document 1). 2).

JP 2001-192874 A Special table 2003-511555 gazette

  The cleaning with SPM requires replenishment of hydrogen peroxide water to compensate for the amount of persulfate ions decomposed and reduced. However, since the sulfuric acid concentration is gradually diluted by the addition of hydrogen peroxide, the liquid composition cannot be maintained constant, and the cleaning liquid is discarded and updated every predetermined time or every predetermined processing amount. For this reason, there is a problem that a large amount of chemicals must be stored and discarded. In addition, this method has a limit in the concentration of persulfate ions produced, which leads to a limit in cleaning effect.

  In contrast, the inventors of the present application have developed and proposed a cleaning system that continuously generates persulfate ions by electrolytic treatment of sulfuric acid to recycle sulfuric acid. With this cleaning system, it is possible to peel off and remove attached organic substances such as resist ion-implanted with high energy from an electronic substrate material or the like, which has been difficult to remove by conventional cleaning methods, by omitting a dry process. However, if the material to be cleaned is transferred to the next process in a state where the cleaning in the cleaning system is incomplete, it is difficult to peel and remove organic substances in the subsequent cleaning processes. There is a possibility of lowering. On the other hand, if the cleaning is performed for a long time so that the cleaning is not insufficient, excessive cleaning is often performed, and there is a problem that work efficiency is remarkably lowered.

  The present invention was made against the background of the above circumstances, and by reusing persulfate ions from sulfuric acid by electrochemical action while repeatedly using sulfuric acid, the amount of sulfuric acid used was greatly reduced. In addition, an object of the present invention is to provide a sulfuric acid recycle type cleaning system and a sulfuric acid recycle type cleaning method that enable inspection of the cleaning surface to enable an appropriate cleaning process.

  That is, the invention of the sulfuric acid recycling type cleaning system according to claim 1 includes a cleaning apparatus for cleaning a material to be cleaned using a persulfate ion-containing solution as a cleaning liquid, and the cleaning liquid discharged from the cleaning tank is included in the cleaning liquid. An electrolytic reactor that produces persulfate ions from sulfate ions to produce a persulfate ion-containing solution; a circulation line that circulates the persulfate ion-containing solution between the cleaning device and the electrolytic reactor; and And a cleaning surface inspection device for inspecting the cleaning surface of the cleaning material.

  The sulfuric acid recycling type cleaning system according to claim 2 is the invention according to claim 1, wherein the cleaning surface inspection device can determine the cleaning degree of the material to be cleaned by recognizing adhering contaminants on the cleaning surface. It is characterized by that.

  The sulfuric acid recycling type cleaning system according to claim 3 is the invention according to claim 1 or 2, wherein the cleaning surface inspection device includes an inspection light irradiation unit that irradiates the cleaning surface with inspection light, and the cleaning surface. And an image data acquisition unit that receives the reflected light reflected by the lens and acquires the cleaning surface image data.

  According to a fourth aspect of the present invention, there is provided the sulfuric acid recycling type cleaning system according to the third aspect, wherein the cleaning surface inspection device holds reference image data in advance, and the cleaning surface image data and the reference image data are stored. A cleaning degree determining means for comparing and determining the cleaning degree of the cleaning surface based on the comparison result is provided.

  According to a fifth aspect of the present invention, there is provided the sulfuric acid recycling type cleaning system according to the fourth aspect, wherein the cleaning degree determination means determines the cleaning degree based on a difference between the cleaning surface image data and the reference image data. It is characterized by that.

  The invention of the sulfuric acid recycling type cleaning system according to claim 6 is the cleaning material according to any one of claims 1 to 5, based on the degree of cleaning of the cleaning material determined by the cleaning surface inspection device. A cleaning control means for controlling the cleaning process is provided.

  The invention of the sulfuric acid recycling type cleaning system according to claim 7 is the invention according to claim 6, wherein, when the cleaning control means determines that the degree of cleaning is completion of cleaning, the cleaning material is transferred to the next step. When it is determined that the cleaning degree is incomplete, the cleaning is performed so that the cleaning is performed again with the cleaning time equal to or shorter than the cleaning time in the immediately preceding cleaning process.

  The invention of the sulfuric acid recycling type cleaning system according to claim 8 is the invention according to claim 7, wherein when the cleaning control means determines that the cleaning has not been completed, the cleaning control means determines the cleaning material according to the degree of cleaning of the material to be cleaned. It is characterized in that the cleaning time of the cleaning process for the material to be cleaned is set again.

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

  The invention of the sulfuric acid recycling type cleaning system according to claim 10 is characterized in that, in the invention according to any one of claims 1 to 9, the material to be cleaned is a semiconductor substrate.

  The invention of the sulfuric acid recycling type cleaning method according to claim 11 is a solution containing persulfate ions by generating persulfate ions from sulfate ions contained in the solution by an electrolytic reaction when the material to be cleaned is cleaned by a multi-stage cleaning process. And cleaning the material to be cleaned using the persulfate ion-containing solution as a cleaning liquid, and subjecting the cleaning liquid to the electrolytic reaction again, repeatedly regenerating the persulfate ion-containing solution for the cleaning liquid, The cleaning surface of the cleaned material to be cleaned is inspected, and when it is determined that the cleaning surface is not clean as a result of the inspection, cleaning with the cleaning liquid is performed again. In this case, the cleaning time for re-cleaning can be set appropriately depending on the degree of cleaning, and the cleaning can be performed in a time shorter than the cleaning time for the first cleaning.

  That is, according to the present invention, the persulfate ions in the cleaning liquid are self-decomposed to generate oxidizing power. In the material to be cleaned that is in contact with the cleaning liquid, contaminants are effectively peeled and removed by the action of sulfuric acid and persulfate ions, and the contaminants that have moved into the cleaning liquid are decomposed by the action of persulfate ions. And in a washing | cleaning liquid, a persulfate ion density | concentration falls gradually, when the persulfate ion in a solution self-decomposes. This persulfate ion-containing solution is sent to the electrolytic reaction apparatus through a circulation line. In an electrolytic reaction apparatus, an anode and a cathode are immersed in a solution containing sulfate ions, and a current is passed between the electrodes to perform electrolysis, whereby sulfate ions are oxidized to produce persulfate ions, and a persulfate ion concentration is sufficiently high. Regenerated to a sulfate ion-containing solution. The regenerated persulfate ion-containing solution is returned to the cleaning device through the circulation line, and the material to be cleaned is effectively peeled and cleaned with a high concentration of persulfate ions in the same manner as described above. By repeatedly circulating the persulfate ion-containing solution between the cleaning device and the electrolytic reaction device, effective cleaning can be continued while maintaining the persulfate ion concentration.

  In addition, as the temperature of persulfate ions increases, the self-decomposition rate increases and a high peeling cleaning action is obtained. At a high temperature such as 130 ° C., the self-decomposition rate becomes very fast with a half-life of about 5 minutes. On the other hand, in the electrolytic reaction apparatus, the lower the solution temperature, the better the production efficiency of persulfate ions 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 175 ° C. Below this temperature range, the effect of peeling and cleaning by persulfate ions decreases. On the other hand, when the temperature exceeds 175 ° C., the self-decomposition rate of persulfate ions becomes extremely high and the resist cannot be oxidized sufficiently, so that the appropriate temperature of the cleaning liquid is within the above range.

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 cleaning solution can be adjusted by exchanging heat with each other when the persulfate ion-containing solution is sent from one device to the other device through a circulation line. . That is, a persulfate ion-containing solution (return solution) that is relatively heated and sent from the cleaning device to the electrolytic reaction device, and an excessive solution that is relatively lowered in temperature and sent from the electrolytic reaction device to the cleaning device. When heat exchange with the sulfate ion-containing solution (feed solution) is performed, the temperature of the return liquid having a high temperature is reduced due to heat being removed by the heat exchange, and the temperature is adjusted to be desirable as an electrolysis solution for the electrolytic reaction apparatus. The 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 persulfate ions 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 solution electrolyzed in 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, persulfate ion generation efficiency increases as the sulfuric acid concentration decreases. On the other hand, when the sulfuric acid concentration is lowered, the solubility of an organic compound such as a resist is lowered, and it is difficult to peel off the material to be cleaned. From these viewpoints, the sulfuric acid concentration of the solution used in the system is preferably in the range of 8M to 18M, for example. For the same reason, it is more desirable that the lower limit is 12M and the upper limit is 17M.

  In the electrolytic reaction apparatus, electrolysis is performed by pairing an anode and a cathode. The material of these electrodes is not limited to a specific one in the present invention. However, when platinum, which is widely used as an electrode, is used as 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 diamond electrode can efficiently generate persulfate ions and has little electrode wear. Therefore, among the electrodes of the electrolytic reaction apparatus, it is desirable that at least one electrode, in particular, at least the anode capable of generating sulfate ions is constituted by a diamond electrode, and it is more desirable that both the anode and the cathode are constituted by diamond electrodes.

  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), 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.
Although the cleaning apparatus can cope with either a single wafer type or a batch type, in the cleaning apparatus, a soluble TOC is generated in the cleaning liquid along with the separation and dissolution of contaminants such as resist when the electronic substrate is cleaned. At this time, since it is necessary to efficiently remove the TOC of the cleaning liquid and prevent the organic matter from reattaching to the electronic substrate material, the TOC generation rate [g / l / hr] generated along with the resist peeling and dissolution in the cleaning apparatus is increased. On the other hand, it is desirable to set the electrolysis conditions so that the persulfate ion production rate [g / l / hr] in the electrolytic reaction apparatus is 10 to 500 times. Thereby, consumption and generation of persulfate ions are balanced, and efficient cleaning and efficient electrolytic treatment are performed. For the same reason, it is desirable to set the lower limit to 20 and the upper limit to 300.

Since the persulfate ion has a high oxidation resolution as described above, it is highly effective in removing organic contaminants from the electronic material substrate. However, depending on the state of contamination of organic matter such as organic matter on the surface to be cleaned, the organic matter on the cleaning surface may not be completely removed within the prescribed processing time. When the material to be cleaned is conveyed to the next cleaning step, a mixed solution of ammonia and hydrogen peroxide solution (SC-1) or a mixed solution of hydrochloric acid and hydrogen peroxide solution (SC-2) generally called RCA cleaning. The cleaning process is performed. In this RCA cleaning process, organic contaminants such as a resist adhered firmly cannot be peeled and removed, which ultimately leads to a decrease in product yield. In addition, after washing with persulfate ions, rinsing with ultrapure water or the like may be performed. In such cases, washing with persulfate ions may not be performed properly. turn into. If the cleaning with persulfate ions is performed for a sufficient time in consideration of variations in the cleaning results, the above-described problem of poor cleaning can be avoided. However, the material to be cleaned that has been cleaned at an early stage is cleaned over a long period of time, resulting in a decrease in work efficiency.
In the present invention, by providing a cleaning surface inspection device that inspects the cleaning surface of the material to be cleaned, the cleaning surface of the material to be cleaned once inspected can be inspected to determine the degree of cleaning. By recognizing the degree of cleaning, it is possible to select recleaning, conveyance of a material to be cleaned to the next process, or the like. As a result, an appropriate operation is selected depending on the degree of cleaning of the material to be cleaned.Therefore, when cleaning the material to be cleaned for the first time, it is not necessary to set the cleaning time longer than necessary, and standard contamination is made. The cleaning time can be determined assuming the material to be cleaned.

  In general, in order to observe the surface properties of an object to be inspected, as shown in Japanese Patent Laid-Open No. 10-103916 and Japanese Patent No. 3558203, the surface to be cleaned is irradiated with inspection illumination light, and image light from the surface to be cleaned is irradiated. A method has been proposed in which image data is captured by a CCD camera and displayed on a monitor, and an observer visually recognizes the defect and creates standard data. However, although these methods are useful for finding defective products and preparing standard data, they have not been proposed for use in performing appropriate cleaning when cleaning a material to be cleaned.

In the present invention, visible light, infrared light, or the like can be used as the irradiation light for inspection. However, the type of irradiation light is not particularly limited as the present invention. Further, the configuration of the inspection light irradiation unit that irradiates the inspection light is not particularly limited, and an appropriate one such as a lamp, an LED, or a laser can be used.
The inspection light is applied to the surface to be cleaned and reflected by the surface to be cleaned. This reflected light is received by a light receiving unit included in the image data acquisition unit. The light receiving unit can be composed of a light receiving element such as a CCD. The signal obtained by the CCD is subjected to, for example, A / D conversion, and subjected to appropriate image processing such as region discrimination, spatial filter, and density adjustment, and image data is acquired. A series of these processes is performed by the image data acquisition unit. The obtained image data can be stored in an appropriate storage unit such as a memory or HDD.

In the surface inspection apparatus according to the present invention, it is preferable that the image data is used to recognize the adhered contaminants on the cleaning surface and to determine the cleaning degree of the material to be cleaned. The inspection result in the present invention can be judged by an operator, but it is preferable that the surface inspection apparatus has a function of determining whether or not attached organic substances such as a resist are completely removed. .
This function can be performed by the cleaning degree determination means provided in the surface inspection apparatus. Examples of the cleaning degree determination unit include a CPU and a program that operates the CPU, and further includes a storage unit that appropriately stores data.
The degree-of-cleaning determination unit holds image data serving as a reference for determining the degree of cleaning in advance. This image data assumes a clean cleaning surface. In addition, when a pattern-generated semiconductor wafer or the like is to be cleaned, the reference image data includes a pattern image. Therefore, by storing the reference image data corresponding to the material to be cleaned, it is possible to accurately determine the degree of cleaning even for materials to be cleaned of different types.

The cleaning degree determination can be performed by comparing the image data acquired with the image data and reference image data.For example, an image area that is recognized as a contaminated portion is determined from the image data of the inspection image data, and the image area The degree of cleaning can be determined by area ratio or the like. The determination of the degree of cleaning may be merely to distinguish between completion of cleaning and incomplete cleaning, and the degree of cleaning may be further distinguished when the cleaning is incomplete.
The degree of cleaning can be appropriately quantified, and the degree of cleaning can be determined according to the numerical value when the cleaning is completed or not completed. In this determination, reference cleanliness reference data can be defined in advance, and the cleanliness can be determined by comparing the reference data with the cleanliness data obtained by measurement.

Moreover, in this invention, the control part which controls a washing | cleaning process based on a washing | cleaning degree can be provided.
In the control unit, when the cleaning degree is determined to be cleaning completion, the cleaning process is terminated, and the material to be cleaned is transferred to the next process. If it is determined that the cleaning is not sufficient and the cleaning is not completed, the cleaning in the cleaning process is performed again. At this time, since many contaminants have been removed by the immediately preceding cleaning process, it is sufficient to perform the cleaning with a shorter cleaning time than the immediately preceding cleaning process. It is desirable to set the time. In setting the cleaning time, the cleaning time can be determined based on the degree of cleaning. In other words, the less contaminated material remains, the shorter the cleaning time can be avoided. It should be noted that inspection, determination of the degree of cleaning, and re-cleaning as necessary can be performed repeatedly.

  In addition, in a subsequent process of the cleaning process using the persulfate ions, an appropriate cleaning process or rinsing process can be performed. In the present invention, the contents of these steps are not particularly limited. For example, a cleaning process using the above-described SC-1, SC-2 solution or dilute hydrofluoric acid can be used.

  As described above, according to the sulfuric acid recycle type cleaning system of the present invention, a cleaning apparatus for cleaning a material to be cleaned using a persulfate ion-containing solution as a cleaning liquid, and persulfate ions from sulfate ions contained in the solution by electrolytic reaction. An electrolytic reaction device that produces a persulfate ion-containing solution, a circulation line that circulates the persulfate ion-containing solution between the cleaning device and the electrolytic reaction device, and a cleaning surface of the material to be cleaned In addition, the persulfate ion-containing solution for repeatedly using the sulfuric acid solution and enhancing the peeling effect can be regenerated on site by the electrolytic reaction device and used for cleaning. After cleaning once, the cleaning surface of the material to be cleaned is inspected by the cleaning surface inspection device, so that the cleaning degree of the cleaning material is recognized, and based on this cleaning degree, the end of cleaning and the continuation of cleaning are determined. Properly perform efficient cleaning work. That is, a decrease in product yield can be suppressed. Further, until now, the processing time has been set longer than the necessary time in order to completely remove the contaminants, but it is not necessary to make the processing time longer and the throughput can be improved.

Below, one Embodiment of this invention is described based on FIG. In addition, embodiment described below is one form of this invention, and does not limit this invention.
The sulfuric acid recycling type cleaning system of the present invention includes a cleaning apparatus including a single wafer cleaning tank 1, an electrolytic reaction apparatus including electrolytic reaction tanks 20 and 25, and a circulation including return pipes 10a and 10b and feed pipes 11a and 11b. The line is the main component.
In the cleaning device, a liquid spray nozzle 2 is provided as a droplet jet forming device, and a tip side ejection portion of the liquid spray nozzle 2 is located in the cleaning tank 1. Connected to the liquid spray nozzle 2 are a return pipe 10b of a circulation line for circulating a persulfate ion-containing solution 16 to and from an electrolytic reaction apparatus, which will be described later, and an N ₂ gas supply pipe 3. The liquid spray nozzle 2 mixes the persulfate ion-containing solution 16 supplied from the return pipe 10b with the high-pressure N ₂ gas supplied from the N ₂ gas supply pipe 3, and the persulfate ion-containing solution 16 is mixed. The liquid droplets are ejected downward. The return pipe 10b is provided with a heating device 19 immediately before the connection portion of the liquid spray nozzle 2, and the persulfate ion-containing solution 16 supplied to the liquid spray nozzle 2 is preferably 100 to 180 ° C. Heat to.

In the cleaning tank 1, a substrate holder 4 is installed as a member to be cleaned holding means in the ejection direction of the liquid spray nozzle 2. A semiconductor substrate 30 as a material to be cleaned is placed on the substrate holder 4. It is desirable that the substrate holder 4 or the liquid spray nozzle 2 be relatively movable so that the liquid droplets uniformly hit the surface of the substrate 30. Further, a transfer device 29 for transferring the substrate 30 into and out of the cleaning tank is provided.
Further, inside the cleaning tank 1, a light receiving / emitting unit 27 is provided for irradiating the semiconductor substrate 30 cleaned in the cleaning tank 1 with inspection light and receiving the reflected light. 27 is connected to a control device 28 outside the cleaning tank 1 to constitute the cleaning surface inspection device of the present invention.

  Further, a feed pipe 11a of a circulation line is connected to the drainage part of the cleaning tank 1, and a feed pump 12 for feeding a persulfate ion-containing solution is interposed in the feed pipe 11a. . A heat exchanger 13 that performs heat exchange is disposed between the return pipe 10b and the feed pipe 11a on the downstream side of the liquid feed pump 12, and is connected to the solution storage tank 14 on the downstream side. An ultrapure water supply line 15 for supplying ultrapure water is connected to the solution storage tank 14. One end of the feed pipe 11 b is further connected from the solution storage tank 14, and the other end of the feed pipe 11 b is connected to the inlet side of the electrolytic reaction tank 20 via the liquid feed pump 17.

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

The electrolytic reaction tank 20 is configured so that the solution passes between the electrodes. A connecting pipe 23 is connected to the outlet side of the electrolytic reaction tank 20, and the other end is the inlet side of the electrolytic reaction tank 25. It is connected to the.
The electrolytic reaction tank 25 has the same configuration as that of the electrolytic reaction tank 20, and an anode 26a and a cathode 26b are arranged. Further, a bipolar electrode 26c... Has a predetermined interval between the anode 26a and the cathode 26b. 26c is arranged. The DC power source 22 is also connected to the anode 26a and the cathode 26b.

In this embodiment, the electrodes 21a, 21b, 21c, 26a, 26b, and 26c are constituted by diamond electrodes. The diamond electrode is manufactured by forming a diamond thin film on a substrate and doping boron in a range of preferably 50 to 20,000 ppm with respect to the carbon content of the diamond thin film. Alternatively, a self-stand type may be used by removing the substrate after forming the thin film.
A return pipe 10 a is connected to the outlet side of the electrolytic reaction tank 25. That is, the electrolytic reaction apparatus is constituted by the electrolytic reaction tanks 20 and 25, the DC power supply 22 and the connecting pipe 23 connected in series.

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

Next, details of the above-described cleaning surface inspection apparatus will be described with reference to FIG.
The light emitting / receiving unit 27 includes an inspection light irradiating unit 271 that irradiates the cleaned semiconductor substrate 30 with inspection light, and a light receiving unit 272 that receives the reflected light reflected by the semiconductor substrate 30. The inspection light irradiation unit 271 is configured by a lamp or the like, and the light receiving unit 272 is configured by a light receiving element such as a CCD.
The control device 28 includes a control unit 280 that controls the entire cleaning system, and the control unit 280 mainly includes a CPU and a program for operating the CPU. The control unit 280 controls the transfer device 29 described above to carry the semiconductor substrate 30 into the cleaning tank 1 or to transfer the cleaned semiconductor substrate to the next process (not shown). In addition, the control unit 280 may control the liquid spray nozzle 2, the pumps 12, 17, 18 or the DC power source 22 to control the circulation and injection of the persulfate ion-containing solution to execute and end the cleaning process. it can.

  In addition, the control device 28 is provided with a storage unit 281 that can read and write data by the control unit 280. The storage unit 281 can be configured by a flash memory, a RAM, an HDD, or the like, and may include a plurality of types of storage media. In the storage unit 281, reference image data assuming a clean cleaning surface of the semiconductor substrate 30 to be cleaned is stored in advance. The reference image data is prepared so as to include the pattern as an image when the semiconductor substrate 30 on which the pattern has been formed is to be cleaned.

  An irradiation unit driving unit 270 is connected to the control unit 280, and the irradiation unit driving unit 270 is connected to the inspection light irradiation unit 271 so as to drive the inspection light irradiation unit 271 described above. Thereby, the irradiation on / off of the inspection light irradiation unit 271 can be controlled by the control unit 280. An image processing unit 274 is connected to the control unit 280, and an A / D conversion unit 273 connected to the light receiving unit 272 is connected to the image processing unit 274. As a result, the image data received by the light receiving unit 272 and subjected to image processing is input to the control unit 280. The light receiving unit 272, the A / D conversion unit 273, and the image processing unit 274 constitute an image data acquisition unit of the present invention. The control unit 280 is configured to determine the degree of cleaning of the semiconductor substrate 30 by comparing the inspection image data with the reference image data stored in the storage unit, and the CPU configuring the control unit 280 and the CPU The program that operates the functions as the cleaning degree determination means of the present invention.

Next, the operation of the sulfuric acid recycling type single wafer cleaning system having the above configuration will be described with reference to the flowchart of FIG.
At the start of cleaning, the transfer device 29 is operated under the control of the control unit 280 to transfer the semiconductor substrate 30 from the outside of the cleaning tank 1 onto the substrate holder 4 of the cleaning tank 1. Further, the control unit 280 controls each part of the cleaning system to start cleaning. At this time, control is performed so that cleaning is performed based on a predetermined cleaning time. The reference cleaning time can be stored as data in the storage unit 281, for example, and can be initialized by reading the data by the control unit 280 during cleaning (step S <b> 1).

In the washing process (step S2), sulfuric acid is accommodated in the solution storage tank 14, and ultrapure water is mixed into the solution storage tank 14 from the ultrapure water supply line 15 at a predetermined volume ratio to obtain a sulfuric acid solution having a sulfuric acid concentration of 10 to 18M. And This is sequentially fed to the electrolytic reaction tank 20 by the liquid feed pump 17. In the electrolytic reaction tank 20, when the anode 21a and the cathode 21b are energized by the DC power source 22, the bipolar electrodes 21c... 21c are polarized, and the anode and the cathode appear at predetermined intervals. The solution sent to the electrolytic reaction tank 20 is passed between these electrodes. At this time, it is desirable to set the output of the liquid feed pump 17 so that the liquid flow rate is 1 to 10,000 m / hr. In the above energization, it is desirable to control the energization so that the current density on the diamond electrode surface is 10 to 100,000 A / m ² .

  When the solution is energized in the electrolytic reaction tank 20, the sulfate ions in the solution undergo an oxidation reaction to generate persulfate ions, and a high concentration persulfate ion-containing solution 16 is obtained. The persulfate ion-containing solution 16 is further sent from the connecting pipe 23 to the electrolytic reaction tank 25 and is energized by the DC power source 22 in the same manner as the electrolytic reaction tank 20 to generate persulfate ions. The persulfate ion-containing solution 16 having a high concentration in this way is temporarily stored in the solution storage tank 14 through the return pipe 10a. The persulfate ion-containing solution 16 stored in the solution storage tank 14 is fed to the cleaning tank 1 side by the liquid feed pump 18 through the return pipe 10b. The persulfate ion-containing solution 16 to be fed passes through the heat exchanger 13 where the heat is exchanged with the solution in the feed tube 11a fed from the washing tank 1 toward the solution storage tank 14 and then rises. Warm up. The persulfate ion-containing solution 16 is further fed to the washing tank 1 side, heated to 100 to 150 ° C. by the heating device 19, and supplied to the liquid spray nozzle 2.

In the washing tank 1, the heated persulfate ion-containing solution and the N ₂ gas are mixed in the liquid spray nozzle 2, and high-temperature persulfate ion-containing droplets are ejected for a certain period of time.
A semiconductor substrate 30 is installed on the substrate holder 4. The semiconductor substrate 30 is rotated by the substrate holder 4, and the surface of the semiconductor substrate 30 is cleaned by the persulfate ion-containing droplets. The resist is peeled off and removed by the action of sulfate ions. The ejected persulfate ion-containing solution 16 scatters and falls after the semiconductor substrate 30 is washed, and is discharged to the feed tube 11a together with the dissolved resist and the like. In the feed pipe 11a, the persulfate ion-containing solution 16 is fed to the solution storage tank 14 side by the liquid feed pump 12. In this case, heat is exchanged with the return pipe 10b by the heat exchanger 13 to lower the temperature of the persulfate ion-containing solution, and the temperature is gradually lowered by natural cooling. The temperature is in the range of 90 ° C. Thereafter, it is temporarily stored in the solution storage tank 14. In addition, when it is desired to reliably lower the temperature, a cooling means for forcibly cooling the solution storage tank 14 by water cooling or air cooling may be provided. When the liquid is fed through the feed pipe 11a, the dissolved resist material peeled and removed in the cleaning tank 1 is decomposed. Moreover, in the solution storage tank 14, the temperature of the solution has fallen by the said heat exchange, and the self-decomposition is suppressed. Further, when the solution is temporarily stored in the solution storage tank 14, the decomposition of the resist melt proceeds, and the inflow of the resist melt into the electrolytic reaction apparatus is effectively prevented.

In the solution storage tank 14, TOC is generated as the resist and other contaminants are peeled and dissolved in the single wafer cleaning apparatus. This TOC can be measured by a TOC measuring device (not shown) or the like, and the TOC increase rate can be calculated based on the temporal change of the measurement result.
Based on the TOC increase rate, in the electrolytic reaction tanks 20 and 25, (persulfate ion generation rate [g / l / hr]) / (TOC increase rate in cleaning solution tank [g / l / hr]) is 10 to 500. The electrolysis conditions are set so as to satisfy the above. The electrolysis conditions can be set by adjusting the current density, the liquid flow rate, and the solution temperature.

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

When the cleaning for the predetermined cleaning time is completed in the cleaning process, the ejection of the persulfate ion-containing solution 16 from the liquid spray nozzle 2 is stopped, and the cleaning surface inspection of the semiconductor substrate 30 by the cleaning surface inspection apparatus is started. (Step S3).
In this process, the irradiation unit driving unit 270 is controlled by a command from the control unit 280, and the inspection light is applied to the cleaning surface of the semiconductor substrate 30 from the inspection light irradiation unit 271. The inspection light may scan the semiconductor substrate or the light receiving and emitting unit so that the entire cleaning surface is irradiated.
The inspection light is reflected by the cleaning surface, and the reflected light is received by the light receiving unit 272. The reflected light is in accordance with the adhesion of patterns and contaminants depending on the properties of the cleaning surface. The reflected light is output as an electrical signal by the light receiving unit 272 and output to the A / D conversion unit 273. After being binarized by the A / D conversion unit 273, it is input to the image processing unit 274, and the image processing unit 274 performs appropriate image processing to obtain inspection image data. The inspection image data is an image of the cleaning surface of the semiconductor substrate 30 and is an image according to the surface properties. The inspection image data is output to the control unit 280. The control unit 280 reads the reference image data stored in the storage unit 281 and compares it with the inspection image data described above. As a result of the comparison, a contaminated area that is determined to be a contaminated part from the difference in the data is recognized. The area ratio of the contaminated area is calculated, and the degree of cleaning is determined based on a predetermined standard (step S4).

When it is determined in the cleaning degree determination process that the cleaning degree is complete, it is assumed that the necessary cleaning using the persulfate ion-containing solution is completed, and the semiconductor device 30 is removed from the cleaning tank 1 by controlling the transfer device 29. Then, it is transferred to the next RCA cleaning process or the like (step S6), and the cleaning is finished. If another lot needs to be cleaned, the same cleaning process as described above is continued for the other semiconductor substrate 30.
On the other hand, when it is determined that the cleaning has not been completed in the cleaning degree determination step, a cleaning time for performing cleaning again is set (step S5). In this setting, the cleaning time can be determined according to the determined degree of cleaning. That is, when the degree of cleaning is low and the degree of contamination is high, a long cleaning time is set, and when the degree of cleaning is relatively high and the degree of contamination is low, a short cleaning time is set. In any case, since the degree of contamination is lower than that at the beginning due to the last washing, a washing time shorter than the washing time determined in the last washing can be set. If the cleaning has not been completed, a cleaning time shorter than the immediately preceding cleaning time may be uniformly determined. In addition, when setting the cleaning time according to the cleaning degree, the storage unit stores a plurality of reference cleaning degrees and the cleaning time in association with each other, and stores the data as appropriate by reading these data as appropriate. The corresponding cleaning time can be set easily.
After setting the cleaning time, the process proceeds to step S2 described above to perform a cleaning process, and further, a cleaning surface inspection is performed to determine the cleaning degree. By repeating this, it is possible to avoid performing the cleaning process in an excessively long time, and it is possible to perform the cleaning with a high degree of cleanliness.

In the above embodiment, a part of the surface inspection device (light emitting / receiving unit) is installed inside the cleaning tank, but after the surface inspection device is installed outside the cleaning device and the material to be cleaned is cleaned, It is also possible to transfer to here and inspect the surface to be cleaned.
Further, in the above embodiment, a sheet type device has been described as the cleaning device. However, a batch type cleaning device may be used. In the batch type cleaning device, the material to be cleaned immersed in the cleaning tank is ultrapure. It is also possible to inspect the surface to be cleaned by rinsing with water and transporting it to a surface inspection apparatus installed outside the cleaning apparatus.

Using the cleaning system shown in FIG. 1, a high concentration sulfuric acid solution prepared in a ratio of 40 L of 97% sulfuric acid and 8 L of ultrapure water was stored in the solution storage tank 14. In the electrolytic reaction apparatus, two electrolytic reaction apparatuses each incorporating 10 boron-doped conductive diamond electrodes having a diameter of 15 cm and a thickness of 0.5 mm were arranged in series. Effective anode area for electrolysis is 30dm ^2, and electrolysis by setting the current density 30A / dm ^2. At this time, it was confirmed that the persulfate ion production rate was 3 g / L / h in the electrolytic reaction apparatus. A cleaning solution containing persulfate ions from a solution storage tank is supplied to a single wafer cleaning device at 2 L / min. Then, the liquid was fed to the fluid spray nozzle 2 by heating to about 130 ° C. with a heating device. Resist-coated 6-inch silicon wafer held by the substrate holder 4 is added for 3 min. / Washed at a rate of about 1 sheet. The washing waste liquid was collected in a solution storage tank. The silicon wafer cleaned by the single wafer cleaning apparatus is further treated with ultrapure water for 1 min. Rinse at a rate of about 1 sheet / spin and spin dry. At this time, the image data of the silicon wafer was captured by the surface inspection device and transferred to the control device.

The control device inspected whether or not the resist was completely removed from the cleaned surface of the silicon wafer by comparing with the image data of the silicon wafer in which the resist was completely removed and confirmed to be clean. It should be noted that the silicon wafer determined to be not clean is again cleaned by this cleaning apparatus for 2 min. The system was set up to perform rewashing at a rate of 1 / sheet. When cleaning is normally completed, the processing time is about 5 minutes for one silicon wafer including the rinsing process, and when the cleaning is repeated twice, the processing time is about 8 minutes. The silicon wafer subjected to such cleaning was brought into a wafer analyzer, heated to 400 ° C., and the organic residue was measured with a mass spectrometer. The residue was about ²⁰⁰ to 300 pg / cm ² , and a highly clean wafer was obtained. It was confirmed that it was obtained. Furthermore, when the periphery of the pattern was observed with a scanning electron microscope with a low acceleration voltage, no resist residue was confirmed. Such a cleaning process was continuously performed for 8 hours to obtain 90 silicon wafers. Among these, there were nine wafers in which the controller was activated and the cleaning process was repeated twice. As a result of measuring organic residues on the 90 silicon wafers after cleaning with the above-described wafer analyzer and mass spectrometer, the organic residues on all silicon wafers are 300 pg / cm ² or less, and the resist is completely peeled off. A clean wafer was obtained. During this time, no new chemical was added, and the TOC concentration of the cleaning liquid in the solution storage tank was below the detection limit.

(Comparative Example 1)
The 6-inch silicon wafer coated with the resist was cleaned at the same cleaning process and speed without operating the cleaning surface inspection device and the control device under the same conditions as the cleaning device of Example 1. Such a cleaning process was continuously performed for 8 hours to obtain 96 silicon wafers.
During this time, no new chemical was added, and the TOC concentration of the cleaning liquid in the solution storage tank was below the detection limit. As a result of measuring the organic residues on the 96 silicon wafers after the cleaning with the above-described wafer analyzer and mass spectrometer, the organic residues on the 87 silicon wafers were 300 pg / cm ² or less, and the resist was completely removed. Although clean exfoliated wafers could be obtained, organic residues of 5000 pg / cm ² or more were detected in 9 sheets. Further, when these silicon wafers were observed on the surface with a scanning microscope with a low acceleration voltage, adhering organic substances considered to be resist residues were confirmed around the pattern.
Thus, in the absence of the surface inspection device and the control device, a silicon wafer that has not been cleaned in a normal processing time is brought into the next process, resulting in a decrease in yield of the semiconductor manufacturing process.

(Comparative Example 2)
The 6-inch silicon wafer coated with the resist was cleaned in the same cleaning process without operating the cleaning surface inspection device and the control device under the same conditions as the cleaning device of Example 1. The cleaning rate is 5 min. / Sheet, and including the ultrapure water rinsing step and the spin drying step, the processing time for one silicon wafer was about 7.5 minutes. Such a cleaning process was continuously performed for 8 hours to obtain 64 silicon wafers. During this time, no new chemical was added, and the TOC concentration of the cleaning liquid in the solution storage tank was below the detection limit. As a result of measuring organic residues on the above-described 64 silicon wafers with the above-described wafer analyzer and mass spectrometer, the organic residues on all silicon wafers were 300 pg / cm ² or less, and the resist was completely Although a peeled clean wafer could be obtained, the number of processed wafers was greatly reduced as compared with Example 1. Thus, when the cleaning speed is lowered, the throughput of the apparatus is lowered.

It is a figure which shows the sulfuric acid recycle type cleaning system of one Embodiment of this invention. Similarly, it is a partial detail view. Similarly, it is a flowchart which shows a washing | cleaning process process.

Explanation of symbols

1 cleaning tank 2 liquid spray nozzle 3 N ₂ gas supply pipe 4 substrate holder 10a return pipe 10b return pipe 11a feed pipe 11b feed pipe 12 feeding pump 13 heat exchanger 14 solution storage tank 15 ultra-pure water supply line 16 persulfate ions Contained solution 17 Liquid feed pump 18 Liquid feed pump 19 Heating device 20 Electrolytic reaction tank 21a Anode 21b Cathode 21c Bipolar electrode 22 DC power supply 23 Connection pipe 25 Electrolytic reaction tank 26a Anode 26b Cathode 26c Bipolar electrode 27 Light receiving / emitting section 271 Inspection light irradiation section 272 Light-receiving unit 28 Control device 280 Control unit 281 Storage unit 29 Transport device 30 Semiconductor substrate

Claims (11)

  A cleaning apparatus for cleaning the material to be cleaned using a persulfate ion-containing solution as a cleaning liquid, and a persulfate ion-containing solution by electrolyzing the cleaning liquid discharged from the cleaning tank to generate persulfate ions from the sulfate ions contained in the cleaning liquid. An electrolytic reaction device to be manufactured, a circulation line for circulating the persulfate ion-containing solution between the cleaning device and the electrolytic reaction device, and a cleaning surface inspection device for inspecting the cleaning surface of the material to be cleaned A sulfuric acid recycling type cleaning system.   2. The sulfuric acid recycle type cleaning system according to claim 1, wherein the cleaning surface inspection device recognizes adhering contaminants on the cleaning surface and makes it possible to determine the cleaning degree of the material to be cleaned.   The cleaning surface inspection apparatus includes: an inspection light irradiation unit that irradiates the cleaning surface with inspection light; and an image data acquisition unit that receives reflected light reflected by the cleaning surface and acquires cleaning surface image data. The sulfuric acid recycle type cleaning system according to claim 1 or 2, characterized by the above.   The cleaning surface inspection apparatus includes a cleaning degree determination unit that holds reference image data in advance, compares the cleaning surface image data with the reference image data, and determines the cleaning degree of the cleaning surface based on the comparison result. The sulfuric acid recycling type cleaning system according to claim 3, wherein the sulfuric acid recycling type cleaning system is provided.   5. The sulfuric acid recycling type cleaning system according to claim 4, wherein the cleaning degree determination means determines the cleaning degree based on a difference between the cleaning surface image data and the reference image data.   The sulfuric acid according to any one of claims 1 to 5, further comprising a cleaning control means for controlling a cleaning process of the material to be cleaned based on a degree of cleaning of the material to be cleaned which is found by the cleaning surface inspection apparatus. Recyclable cleaning system.   The cleaning control means transports the material to be cleaned to the next process when it is determined that the cleaning degree is completion of cleaning, and when it is determined that the cleaning degree is incomplete cleaning, 7. The sulfuric acid recycle type cleaning system according to claim 6, wherein the sulfuric acid recycling type cleaning system is controlled so that the cleaning is performed again with a cleaning time equal to or shorter than the cleaning time in step.   8. The cleaning control unit according to claim 7, wherein when it is determined that the cleaning has not been completed, the cleaning time for the cleaning process for the cleaning target material is set according to the cleaning degree of the cleaning target material. The sulfuric acid recycling type cleaning system described.   The sulfuric acid recycle type cleaning system according to any one of claims 1 to 8, wherein at least an anode of an electrode provided in the electrolytic reaction apparatus is a conductive diamond electrode.   The sulfuric acid recycling type cleaning system according to claim 1, wherein the material to be cleaned is a semiconductor substrate.   When cleaning a material to be cleaned by a multi-stage cleaning process, a persulfate ion-containing solution is produced by generating persulfate ions from sulfate ions contained in the solution by an electrolytic reaction, and the persulfate ion-containing solution is used as a cleaning solution. Washing the material to be cleaned, subjecting the cleaning liquid to the electrolytic reaction again, regenerating the persulfate ion-containing solution repeatedly, using it as the cleaning liquid, and inspecting the cleaning surface of the material cleaned with the cleaning liquid, As a result, when it is determined that the cleaning surface is not clean, cleaning with the above-described cleaning liquid is performed again.

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